VANGUARD BOND INDEX FUND INC
497, 1998-04-21
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<PAGE>   1
 
================================================================================
 
                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549
 
                                   FORM N-1A
                   REGISTRATION STATEMENT (NO. 33-6001) UNDER
                           THE SECURITIES ACT OF 1933
                          PRE-EFFECTIVE AMENDMENT NO.                        [ ]
                        POST-EFFECTIVE AMENDMENT NO. 17                      [X]
                                      AND
 
              REGISTRATION STATEMENT UNDER THE INVESTMENT COMPANY
                                  ACT OF 1940
                                AMENDMENT NO. 19                             [X]
                         VANGUARD BOND INDEX FUND, INC.
               (EXACT NAME OF REGISTRANT AS SPECIFIED IN CHARTER)
 
                     P.O. BOX 2600, VALLEY FORGE, PA 19482
                    (ADDRESS OF PRINCIPAL EXECUTIVE OFFICE)
 
                  REGISTRANT'S TELEPHONE NUMBER (610) 669-1000
 
                         RAYMOND J. KLAPINSKY, ESQUIRE
                                  P.O. BOX 876
                             VALLEY FORGE, PA 19482
 
               IT IS PROPOSED THAT THIS FILING BECOME EFFECTIVE:
             April 17, 1998, pursuant to paragraph (b) of Rule 485.
 
                 APPROXIMATE DATE OF PROPOSED PUBLIC OFFERING:
  As soon as practicable after this Registration Statement becomes effective.
 
     WE HAVE ELECTED TO REGISTER AN INDEFINITE NUMBER OF SHARES PURSUANT TO
REGULATION 24f-2 UNDER THE INVESTMENT COMPANY ACT OF 1940. REGISTRANT FILED ITS
RULE 24f-2 NOTICE FOR THE PERIOD ENDED DECEMBER 31, 1997 ON MARCH 30, 1998.
 
================================================================================
<PAGE>   2
 
                         VANGUARD BOND INDEX FUND, INC.
 
                             CROSS REFERENCE SHEET
 
<TABLE>
<CAPTION>
   FORM N-1A
  ITEM NUMBER                                                                LOCATION IN PROSPECTUS
<C>           <S>                                                     <C>
    Item 1.   Cover Page...........................................   Cover Page
    Item 2.   Synopsis.............................................   Fund Expenses
    Item 3.   Condensed Financial Information......................   Financial Highlights; Yield and Total
                                                                      Return
    Item 4.   General Description of Registrant....................   Highlights; Investment Objective;
                                                                      Investment Limitations; Investment
                                                                      Policies; Investment Risks; General
                                                                      Information
    Item 5.   Management of the Funds..............................   Management of the Fund; Investment
                                                                      Adviser; General Information
   Item 5A.   Management's Discussion of Fund Performance..........   Herein incorporated by reference to
                                                                      Registrant's Annual Report to
                                                                      Shareholders dated December 31, 1997,
                                                                      filed with the Securities and
                                                                      Exchange Commission's EDGAR system on
                                                                      March 5, 1998
    Item 6.   Capital Stock and Other Securities...................   Opening an Account and Purchasing
                                                                      Shares; Selling Your Shares; The
                                                                      Share Price of each Portfolio;
                                                                      Dividends, Capital Gains, and Taxes;
                                                                      General Information
    Item 7.   Purchase of Securities Being Offered.................   Cover Page; Opening an Account and
                                                                      Purchasing Shares
    Item 8.   Redemption or Repurchase.............................   Selling Your Shares
    Item 9.   Pending Legal Proceedings............................   Not Applicable

   FORM N-1A                                                                  LOCATION IN STATEMENT
  ITEM NUMBER                                                               OF ADDITIONAL INFORMATION

   Item 10.   Cover Page...........................................   Cover Page
   Item 11.   Table of Contents....................................   Cover Page
   Item 12.   General Information and History......................   Not Applicable
   Item 13.   Investment Policies..................................   Investment Policies; Investment
                                                                      Limitations
   Item 14.   Management of the Registrant.........................   Management of the Fund
   Item 15.   Control Persons and Principal Holders of
              Securities...........................................   Not Applicable
   Item 16.   Investment Advisory and Other Services...............   Management of the Fund
   Item 17.   Brokerage Allocation.................................   Portfolio Transactions
   Item 18.   Capital Stock and Other Securities...................   Not Applicable
   Item 19.   Purchase, Redemption and Pricing of Securities Being
              Offered..............................................   Purchase of Shares; Redemption of
                                                                      Shares
   Item 20.   Tax Status...........................................   Not Applicable
   Item 21.   Underwriters.........................................   Not Applicable
   Item 22.   Calculations of Performance Data.....................   Yield and Total Return
   Item 23.   Financial Statements.................................   Financial Statements
</TABLE>
<PAGE>   3
 
- --------------------------------------------------------------------------------
 
================================================================================
 
[VANGUARD BOND INDEX LOGO]                        A Member of The Vanguard Group
 
- --------------------------------------------------------------------------------
 
- --------------------------------------------------------------------------------
 
PROSPECTUS -- APRIL 17, 1998
- --------------------------------------------------------------------------------
 
NEW ACCOUNT INFORMATION: INVESTOR INFORMATION DEPARTMENT -- 1-800-662-7447
(SHIP)
- --------------------------------------------------------------------------------
 
SHAREHOLDER ACCOUNT SERVICES: CLIENT SERVICES DEPARTMENT -- 1-800-662-2739
(CREW)
- --------------------------------------------------------------------------------
 
INVESTMENT
OBJECTIVE
AND POLICIES          Vanguard Bond Index Fund, Inc. (the "Fund"), is an
                      open-end diversified investment company designed as an
                      "index fund." The Fund consists of four distinct
                      portfolios: the Total Bond Market, Short-Term Bond,
                      Intermediate-Term Bond and Long-Term Bond Portfolios. Each
                      of the Portfolios invests in fixed-income securities with
                      prescribed maturity and credit quality standards in order
                      to match the investment performance of certain investment
                      grade bond indexes. There is no assurance that a Portfolio
                      will achieve its stated objective. Shares of the Fund are
                      neither insured nor guaranteed by any agency of the U.S.
                      Government, including the FDIC.
- --------------------------------------------------------------------------------
 
OPENING AN
ACCOUNT               To open a regular (non-retirement) account, please
                      complete and return the Account Registration Form. If you
                      need assistance in completing this Form, please call our
                      Investor Information Department. To open an Individual
                      Retirement Account (IRA), please use a Vanguard IRA
                      Adoption Agreement. To obtain a copy of this form, call
                      1-800-662-7447, Monday through Friday, from 8:00 a.m. to
                      9:00 p.m. and Saturday, from 9:00 a.m. to 4:00 p.m.
                      (Eastern time). The minimum initial investment is $3,000
                      or $1,000 for Uniform Gifts/Transfers to Minors Act
                      accounts. For certain investors investing $10 million or
                      more in the Total Bond Market Portfolio, the Fund offers a
                      second class of shares, Total Bond Market Portfolio
                      Institutional Shares, which are offered through a separate
                      prospectus. The Total Bond Market Portfolio and the Total
                      Bond Market Institutional Shares do not have the same
                      expenses; as a result, the two Portfolios' performance
                      could differ. To obtain information on the Total Bond
                      Market Portfolio Institutional Shares, please call
                      1-800-523-8066. The Fund is offered on a no-load basis
                      (i.e., there are no sales commissions or 12b-1 fees).
                      However, the Fund incurs expenses for management,
                      administrative and distribution services. Shareholders in
                      each Portfolio will also incur a $10 annual account
                      maintenance fee, deducted at a rate of $2.50 per quarter
                      from each Portfolio account (waived for balances of
                      $10,000 or more at the time of the quarterly deduction).
- --------------------------------------------------------------------------------
 
ABOUT THIS
PROSPECTUS            This Prospectus is designed to set forth concisely the
                      information you should know about the Fund before you
                      invest. It should be retained for future reference. A
                      "Statement of Additional Information" containing
                      additional information about the Fund has been filed with
                      the Securities and Exchange Commission. This Statement is
                      dated April 17, 1998 and has been incorporated by
                      reference into this Prospectus. A copy may be obtained
                      without charge by writing to the Fund, calling the
                      Investor Information Department at 1-800-662-7447 or
                      visiting the Securities and Exchange Commission's website
                      (www.sec.gov).
- --------------------------------------------------------------------------------
 
TABLE OF CONTENTS
 
<TABLE>
<CAPTION>
                Page                                       Page                                       Page
<S>                                        <C>                                        <C>
Highlights .......................  2      Implementation of                          SHAREHOLDER GUIDE
Fund Expenses ...................  5       Policies ......... 14                      Opening an Account and
Financial                                  Investment                                 Purchasing Shares ............... 24
Highlights ...............  6              Limitations ............ 17                When Your Account Will Be
Yield and Total                            Management of the                          Credited ... 27
Return .............  8                    Fund ............ 18                       Selling Your
FUND INFORMATION                           Investment                                 Shares ................ 28
Investment Objective ..............9       Adviser  ................ 18               Exchanging Your Shares ........... 31
Investment                                 Performance Record ............... 19      Important Information About
Policies ................  9               Dividends, Capital Gains                   Telephone Transactions .......... 32
Investment Risks ................. 11      and Taxes ...................... 20        Transferring
Who Should Invest ................ 14      The Share Price of Each                    Registration ........... 33
                                           Portfolio .... 22                          Statements and
                                           General                                    Reports ............ 33
                                           Information ............... 22             Other Vanguard
                                                                                      Services ........... 34
</TABLE>
 
- --------------------------------------------------------------------------------
 
THESE SECURITIES HAVE NOT BEEN APPROVED OR DISAPPROVED BY THE SECURITIES AND
EXCHANGE COMMISSION NOR HAS THE SECURITIES AND EXCHANGE COMMISSION PASSED UPON
THE ACCURACY OR ADEQUACY OF THIS PROSPECTUS. ANY REPRESENTATION TO THE CONTRARY
IS A CRIMINAL OFFENSE.
- --------------------------------------------------------------------------------
 
- --------------------------------------------------------------------------------
<PAGE>   4
 
                                   HIGHLIGHTS
 
OBJECTIVE AND
POLICIES              The Fund is a no-load, open-end diversified investment
                      company designed as an "index" fund. The Fund consists of
                      four distinct Portfolios, each of which invests in
                      fixed-income securities with prescribed maturity and
                      credit quality standards in order to match the investment
                      performance of certain investment grade bond indexes.
                      There is no assurance that any of the Fund's Portfolios
                      will achieve its stated objective.                  PAGE 9
- --------------------------------------------------------------------------------
 
FOUR SEPARATE
PORTFOLIOS            Investors may choose to invest in any of four Portfolios
                      of the Fund:
 
                      TOTAL BOND MARKET PORTFOLIO -- seeks to match the
                      investment performance of the Lehman Brothers Aggregate
                      Bond Index, a broad market-weighted index which
                      encompasses U.S. Treasury and agency securities,
                      investment grade corporate bonds, international
                      (dollar-denominated) investment grade bonds, and mortgage-
                      backed securities.
 
                      SHORT-TERM BOND PORTFOLIO -- seeks to match the investment
                      performance of the Lehman Brothers Mutual Fund Short (1-5)
                      Government/Corporate Index, a market-weighted index which
                      encompasses U.S. Treasury and agency securities and
                      investment grade corporate and international
                      (dollar-denominated) bonds, with maturities between 1 and
                      5 years.
 
                      INTERMEDIATE-TERM BOND PORTFOLIO -- seeks to match the
                      investment performance of the Lehman Brothers Mutual Fund
                      Intermediate (5-10) Government/Corporate Index, a
                      market-weighted index which encompasses U.S. Treasury and
                      agency securities and investment grade corporate and
                      international (dollar-denominated) bonds, with maturities
                      between 5 and 10 years.
 
                      LONG-TERM BOND PORTFOLIO -- seeks to match the investment
                      performance of the Lehman Brothers Long (10+)
                      Government/Corporate Index, a market-weighted index which
                      encompasses U.S. Treasury and agency securities and
                      investment grade corporate and international
                      (dollar-denominated) bonds, with maturities greater than
                      10 years.                                           PAGE 9
- --------------------------------------------------------------------------------
 
RISK
CHARACTERISTICS       Investors in the Fund are exposed to four types of risk
                      from an investment in fixed-income securities. (1)
                      INTEREST RATE RISK is the potential for fluctuations in
                      bond prices due to changing interest rates. (2) INCOME
                      RISK is the potential for a decline in a Portfolio's
                      income due to falling market interest rates. (3) CREDIT
                      RISK is the possibility that a bond issuer will fail to
                      make timely payments of either interest or principal to a
                      Portfolio. (4) PREPAYMENT RISK (applicable to the Total
                      Bond Market Portfolio which invests in mortgage-backed
                      securities) or CALL RISK (for corporate bonds) is the
                      likelihood that, during periods of falling interest rates,
                      callable securities with high stated interest rates will
                      be prepaid (or "called") prior to maturity, requiring a
                      Portfolio to invest the proceeds at generally lower
                      interest rates.
 
                      The chart on page 3 summarizes interest rate, income,
                      credit and prepayment/call risks for the four Portfolios
                      of the Fund. As shown, interest rate risk should be low
                      for the
 
                                        2
<PAGE>   5
 
                      Short-Term Bond Portfolio, moderate for the Total Bond
                      Market and Intermediate-Term Bond Portfolios, and high for
                      the Long-Term Bond Portfolio.                      PAGE 11
- --------------------------------------------------------------------------------
 
                                             RISK SUMMARY
 
<TABLE>
                               <S> <C>                           <C>         <C>      <C>      <C>         <C>
                               -------------------------------------------------------------------------------
</TABLE>
 
<TABLE>
<CAPTION>
                                                                 INTEREST    INCOME   CREDIT   PREPAYMENT/
                                            PORTFOLIO            RATE RISK    RISK     RISK     CALL RISK
                               <S> <C>                           <C>         <C>      <C>      <C>         <C>
                               -------------------------------------------------------------------------------
                                   Total Bond Market              Medium     Medium    Low       Medium
                                   Short-Term Bond                Low        High      Low       Low
                                   Intermediate-Term Bond         Medium     Medium    Low       Low
                                   Long-Term Bond                 High       Low       Low       Medium
                               -------------------------------------------------------------------------------
</TABLE>
 
- --------------------------------------------------------------------------------
 
   
THE VANGUARD
GROUP                 The Fund is a member of The Vanguard Group of Investment
                      Companies, a group of more than 30 investment companies
                      with more than 95 distinct investment portfolios and total
                      assets in excess of $360 billion. The Vanguard Group, Inc.
                      ("Vanguard"), a subsidiary jointly owned by the Vanguard
                      Funds, provides all corporate management, administrative,
                      distribution, and shareholder accounting services on an
                      at-cost basis to the Funds in the Group. As a result,
                      Vanguard's operating expenses are substantially lower than
                      those of the mutual fund industry.                 PAGE 18
    
- --------------------------------------------------------------------------------
 
INVESTMENT
ADVISER               Vanguard's Fixed Income Group provides investment advisory
                      services on an at-cost basis to the Fund's four
                      Portfolios.                                        PAGE 18
- --------------------------------------------------------------------------------
 
FEES AND EXPENSES     Shareholders in each Portfolio will incur an annual $10
                      maintenance fee which will be deducted from the dividend
                      income of each account. This fee will be waived for
                      shareholders with an account balance of $10,000 or more at
                      the time of the quarterly deduction.                PAGE 5
- --------------------------------------------------------------------------------
 
DIVIDEND POLICY       Each Portfolio declares a dividend each business day based
                      on its ordinary income. Dividends are paid on the first
                      business day of each month. Net capital gains, if any,
                      will be distributed annually. Dividend and capital gains
                      distributions may be received in cash or reinvested in
                      additional shares.                                 PAGE 20
- --------------------------------------------------------------------------------
 
TAXES                 Dividends paid by the Fund's Portfolios are subject to
                      federal, state, and local income taxes. Any capital gains
                      distributions from a Portfolio are subject to federal
                      income tax, as well as any applicable state and local
                      taxes. A sale of shares -- whether by outright redemption,
                      checkwriting redemption or an exchange -- is a taxable
                      event and may result in a capital gain or loss.    PAGE 20
- --------------------------------------------------------------------------------
 
PURCHASING
SHARES                You may purchase shares by mail, wire, or exchange from
                      another Vanguard Portfolio. The minimum initial investment
                      is $3,000 per Portfolio ($1,000 for retirement accounts
                      and Uniform Gifts/Transfers to Minors Act accounts); the
                      minimum for subsequent investments is $100. There are no
                      sales commissions or 12b-1 fees.                   PAGE 24
- --------------------------------------------------------------------------------
 
                                        3
<PAGE>   6
 
SELLING SHARES        You may redeem shares of each Portfolio by mail, telephone
                      or check. Telephone redemption proceeds may be received by
                      mail or by wire. There is no charge for redemptions,
                      except for wire withdrawals under $5,000, which are
                      subject to a $5 charge. Your bank may also impose a fee
                      upon receipt of a wire. Each Portfolio's share price is
                      expected to fluctuate, and at the time of redemption may
                      be more or less than at the time of initial purchase,
                      resulting in a gain or loss.                       PAGE 28
- --------------------------------------------------------------------------------
 
SERVICES TO
SHAREHOLDERS          The Fund offers free checkwriting services (minimum $250
                      per checkwriting draft) for easy access to your account
                      balance.                                           PAGE 28
 
                      The Fund offers two special services: Fund Express, for
                      electronic transfers between the Fund and your bank
                      account; and Tele-Account, for "round-the-clock" telephone
                      access to your Fund account balance and certain
                      transactions.                                      PAGE 33
- --------------------------------------------------------------------------------
 
SPECIAL
CONSIDERATIONS        (1) Each Portfolio may invest a portion of its assets in
                          bond (interest rate) futures contracts and options.
 
                      (2) Each Portfolio may lend its securities.        PAGE 16
- --------------------------------------------------------------------------------
 
                                        4
<PAGE>   7
 
FUND EXPENSES         The following tables illustrate ALL expenses and fees that
                      you would incur as a shareholder of the Fund. The expenses
                      and fees set forth in the table are for the 1997 fiscal
                      year.
 
<TABLE>
<CAPTION>
                                                                 TOTAL BOND   SHORT-TERM   INTERMEDIATE-   LONG-TERM
                                         SHAREHOLDER               MARKET        BOND        TERM BOND       BOND
                                     TRANSACTION EXPENSES        PORTFOLIO    PORTFOLIO      PORTFOLIO     PORTFOLIO
                               <S>                               <C>          <C>          <C>             <C>
                               -------------------------------------------------------------------------------------
                               Sales Load Imposed on
                                 Purchases*....................    None         None          None           None
                               Sales Load Imposed on Reinvested
                                 Dividends.....................    None         None          None           None
                               Redemption Fees**...............    None         None          None           None
                               Exchange Fees...................    None         None          None           None
</TABLE>
 
                       * A portfolio transaction fee, payable directly to the
                         Portfolio, may be imposed on aggregate purchases
                         expected to exceed $50 million for the Total Bond
                         Market Portfolio; $15 million for the Short-Term and
                         Intermediate-Term Bond Portfolios; and $2 million for
                         the Long-Term Bond Portfolio. See the Fund's Statement
                         of Additional Information for further information.
 
                      ** Wire redemptions of less than $5,000 are subject to a
                         $5 processing fee.
 
<TABLE>
<CAPTION>
                                                                 TOTAL BOND   SHORT-TERM   INTERMEDIATE-   LONG-TERM
                                         ANNUAL FUND               MARKET        BOND        TERM BOND       BOND
                                      OPERATING EXPENSES         PORTFOLIO    PORTFOLIO      PORTFOLIO     PORTFOLIO
                               <S>                               <C>          <C>          <C>             <C>
                               -------------------------------------------------------------------------------------
                               Management & Administrative
                                 Expenses+.....................     0.14%        0.14%         0.14%         0.11%
                               Investment Advisory Fees........     0.01         0.01          0.01          0.01
                               12b-1 Fees......................     None         None          None          None
                               Other Expenses
                                 Distribution Costs............     0.03         0.03          0.03          0.03
                                 Miscellaneous Expenses........     0.02         0.02          0.02          0.05
                                                                 -------      -------      ---------       -------
                               Total Other Expenses............     0.05         0.05          0.05          0.08
                                                                 -------      -------      ---------       -------
                                        TOTAL OPERATING
                                          EXPENSES.............     0.20%++      0.20%         0.20%         0.20%
                                                                 =======      =======      =========       =======
                                + For accounts of less than $10,000, each Portfolio assesses an annual account
                                  maintenance fee of $10. This fee is in addition to the expenses set forth above.
                               ++ The Portfolio's Institutional class of shares is offered at an estimated expense
                                  ratio of .10% per year.
</TABLE>
 
                      The purpose of these tables is to assist you in
                      understanding the various costs and expenses that you
                      would bear directly or indirectly as an investor in the
                      Fund.
 
EACH PORTFOLIO
CHARGES A $10 ACCOUNT
MAINTENANCE FEE       Each Portfolio assesses an annual maintenance fee of $10
                      to offset the cost of maintaining smaller accounts. This
                      fee, which is paid directly by shareholders, is deducted
                      at a rate of $2.50 per quarter from the dividend income of
                      each account. See "Dividends, Capital Gains and Taxes" for
                      more information on this fee. The $10 fee amounts to 1.00%
                      on a $1,000 investment in a Portfolio, and 0.33% on a
                      $3,000 investment. This fee will be waived for
                      shareholders with an account balance of $10,000 or more at
                      the time of the quarterly deduction.
 
                                        5
<PAGE>   8
 
                      The following example illustrates the expenses that you
                      would incur on a $1,000 investment over various periods,
                      assuming (1) a 5% annual rate of return and (2) redemption
                      at the end of each period. A $10 annual fee payable on
                      accounts with current balances of less than $10,000 is not
                      included. As noted in the table on page 5, the Portfolios
                      charge no redemption fees of any kind.
 
<TABLE>
<CAPTION>
                                                                        1 YEAR   3 YEARS   5 YEARS   10 YEARS
                                                                        ------   -------   -------   --------
                               <S>                                      <C>      <C>       <C>       <C>
                               Total Bond Market Portfolio............   $ 2       $ 6       $11       $26
                               Short-Term Bond Portfolio..............   $ 2       $ 6       $11       $26
                               Intermediate-Term Bond Portfolio.......   $ 2       $ 6       $11       $26
                               Long-Term Bond Portfolio...............   $ 2       $ 6       $11       $26
</TABLE>
 
                      THIS EXAMPLE SHOULD NOT BE CONSIDERED A REPRESENTATION OF
                      PAST OR FUTURE EXPENSES OR PERFORMANCE. ACTUAL EXPENSES
                      MAY BE HIGHER OR LOWER THAN THOSE SHOWN.
- --------------------------------------------------------------------------------
 
FINANCIAL
HIGHLIGHTS            The following financial highlights information with
                      respect to the Total Bond Market, Short-Term Bond,
                      Intermediate-Term Bond and Long-Term Bond Portfolios, for
                      a share outstanding throughout each period presented, has
                      been derived from financial statements which were audited
                      by Price Waterhouse LLP, independent accountants, whose
                      report thereon was unqualified. This information should be
                      read in conjunction with the Fund's 1997 financial
                      statements and notes thereto, which, together with the
                      remaining portions of the Fund's 1997 Annual Report to
                      Shareholders, are incorporated by reference in the
                      Statement of Additional Information and this Prospectus,
                      and which appear, along with the report of Price
                      Waterhouse LLP, in the Fund's 1997 Annual Report to
                      Shareholders. For a more complete discussion of the Fund's
                      performance, please see the Fund's 1997 Annual Report to
                      Shareholders which may be obtained without charge by
                      writing to the Fund or calling our Investor Information
                      Department at 1-800-662-7447.
 
                                        6
<PAGE>   9
 
   
<TABLE>
<CAPTION>
                                      -------------------------------------------------------------------------------------------
                                                                      TOTAL BOND MARKET PORTFOLIO
                                      -------------------------------------------------------------------------------------------
                                                                        YEAR ENDED DECEMBER 31,
                                      -------------------------------------------------------------------------------------------
                                       1997     1996     1995     1994     1993     1992     1991     1990     1989     1988
- ---------------------------------------------------------------------------------------------------------------------------------
<S>                                   <C>      <C>      <C>      <C>      <C>      <C>      <C>      <C>      <C>      <C>    <C>
NET ASSET VALUE, BEGINNING OF
 YEAR..............................   $ 9.84   $10.14   $ 9.17   $10.06   $ 9.88   $ 9.99   $ 9.41   $ 9.44   $ 9.05   $ 9.20
                                      ------   ------   ------   ------   ------   ------   ------   ------   ------   ------ ---
INVESTMENT OPERATIONS
 Net Investment Income.............     .645     .640     .650     .622     .638     .699     .766     .796     .797     .807
 Net Realized and Unrealized Gain
   (Loss) on Investments...........     .250    (.300)    .970    (.888)    .300    (.018)    .605    (.030)    .390    (.150)
                                       -----    -----    -----    -----    -----    -----    -----    -----    -----    -----
     TOTAL FROM INVESTMENT
       OPERATIONS..................     .895     .340    1.620    (.266)    .938     .681    1.371     .766    1.187     .657
- ---------------------------------------------------------------------------------------------------------------------------------
DISTRIBUTIONS
 Dividends from Net Investment
   Income..........................    (.645)   (.640)   (.650)   (.622)   (.638)   (.699)   (.766)   (.796)   (.797)   (.807)
 Distributions from Realized
   Capital Gains...................       --       --       --    (.002)   (.120)   (.092)   (.025)      --       --       --
                                       -----    -----    -----    -----    -----    -----    -----    -----    -----    -----
     TOTAL DISTRIBUTIONS...........    (.645)   (.640)   (.650)   (.624)   (.758)   (.791)   (.791)   (.796)   (.797)   (.807)
- ---------------------------------------------------------------------------------------------------------------------------------
NET ASSET VALUE, END OF YEAR.......   $10.09   $ 9.84   $10.14   $ 9.17   $10.06   $ 9.88   $ 9.99   $ 9.41   $ 9.44   $ 9.05
=================================================================================================================================
TOTAL RETURN (1)...................     9.44%    3.58%   18.18%   (2.66)%   9.68%    7.14%   15.25%    8.65%   13.65%    7.35%
=================================================================================================================================
RATIOS/SUPPLEMENTAL DATA
Net Assets, End of Year
 (Millions)........................   $5,129   $2,962   $2,405   $1,731   $1,540   $1,066     $849     $277     $139      $58
Ratio of Total Expenses to Average
 Net Assets........................     0.20%    0.20%    0.20%    0.18%    0.18%    0.20%    0.16%    0.21%    0.24%    0.30%
Ratio of Net Investment Income to
 Average Net Assets................     6.54%    6.54%    6.66%    6.57%    6.24%    7.06%    7.95%    8.60%    8.49%    8.84%
Portfolio Turnover Rate............       39%      39%      36%      33%      50%      49%      31%      29%      33%      21%
(1) Total return figures do not reflect the annual account maintenance fee of $10.
</TABLE>
    
 
   
<TABLE>
<CAPTION>
                                                              -----------------------------------------------------------
                                                                               SHORT-TERM BOND PORTFOLIO
                                                              -----------------------------------------------------------
                                                                         YEAR ENDED DECEMBER 31,              MAR. 1+ TO
                                                              ---------------------------------------------    DEC. 31,
                                                                  1997            1996            1995           1994
- -------------------------------------------------------------------------------------------------------------------------
<S>                                                           <C>             <C>             <C>             <C>
NET ASSET VALUE, BEGINNING OF YEAR..........................     $ 9.92          $10.07          $ 9.50         $10.00
                                                                 ------          ------          ------         ------
INVESTMENT OPERATIONS
 Net Investment Income......................................       .597            .587            .623           .463
 Net Realized and Unrealized Gain
   (Loss) on Investments....................................       .080           (.146)           .570          (.500)
                                                                 ------          ------          ------         ------
     TOTAL FROM INVESTMENT OPERATIONS.......................       .677            .441           1.193          (.037)
- -------------------------------------------------------------------------------------------------------------------------
DISTRIBUTIONS
 Dividends from Net Investment Income.......................      (.597)          (.587)          (.623)         (.463)
 Distributions from Realized Capital Gains..................         --           (.004)             --             --
                                                                 ------          ------          ------         ------
     TOTAL DISTRIBUTIONS....................................      (.597)          (.591)          (.623)         (.463)
- -------------------------------------------------------------------------------------------------------------------------
NET ASSET VALUE, END OF YEAR................................     $10.00          $ 9.92          $10.07         $ 9.50
=========================================================================================================================
TOTAL RETURN (1)............................................       7.04%           4.55%          12.88%         (0.37)%
=========================================================================================================================
RATIOS/SUPPLEMENTAL DATA
Net Assets, End of Year (Millions)..........................         $446          $328              $208             $77
Ratio of Total Expenses to Average Net Assets...............       0.20%           0.20%           0.20%          0.18%*
Ratio of Net Investment Income to
 Average Net Assets.........................................       6.03%           5.93%           6.28%          5.77%*
Portfolio Turnover Rate.....................................         88%++           65%             65%            53%
(1) Total return figures do not reflect the annual account maintenance fee of $10.
 * Annualized.
 + Subscription period for the Portfolio was from January 18, 1994, through February 28, 1994, during which time all
   assets were held in money market instruments.
 ++ Portfolio turnover rate excluding in-kind redemptions was 73%.
</TABLE>
    
 
- --------------------------------------------------------------------------------
 
                                        7
<PAGE>   10
 
   
<TABLE>
<CAPTION>
                                                ---------------------------------------   ---------------------------------------
                                                           INTERMEDIATE-TERM                             LONG-TERM
                                                            BOND PORTFOLIO                            BOND PORTFOLIO
                                                ---------------------------------------   ---------------------------------------
                                                 YEAR ENDED DECEMBER 31,     MAR. 1+ TO    YEAR ENDED DECEMBER 31,     MAR. 1+ TO
                                                --------------------------    DEC. 31,    --------------------------    DEC. 31,
                                                 1997      1996      1995       1994       1997      1996      1995       1994
- ---------------------------------------------------------------------------------------------------------------------------------
<S>                                             <C>       <C>       <C>      <C>          <C>       <C>       <C>      <C>
NET ASSET VALUE, BEGINNING OF YEAR............  $ 9.96    $10.37    $ 9.18     $10.00     $10.08    $10.82    $ 8.96     $10.00
                                                ------    ------    ------     ------     ------    ------    ------     ------
INVESTMENT OPERATIONS
 Net Investment Income........................    .661      .648      .661       .533       .678      .674      .692       .586
 Net Realized and Unrealized Gain
   (Loss) on Investments......................    .240     (.406)    1.217      (.820)      .700     (.731)    1.884     (1.040)
                                                ------    ------    ------     ------     ------    ------    ------     ------
     TOTAL FROM INVESTMENT OPERATIONS.........    .901      .242     1.878      (.287)     1.378     (.057)    2.576      (.454)
- ---------------------------------------------------------------------------------------------------------------------------------
DISTRIBUTIONS
 Dividends from Net Investment Income.........   (.661)    (.648)    (.661)     (.533)     (.678)    (.674)    (.692)     (.586)
 Distributions from Realized Capital Gains....      --     (.004)    (.027)        --         --     (.009)    (.024)        --
                                                ------    ------    ------     ------     ------    ------    ------     ------
     TOTAL DISTRIBUTIONS......................   (.661)    (.652)    (.688)     (.533)     (.678)    (.683)    (.716)     (.586)
- ---------------------------------------------------------------------------------------------------------------------------------
NET ASSET VALUE, END OF YEAR..................  $10.20    $ 9.96    $10.37     $ 9.18     $10.78    $10.08    $10.82     $ 8.96
=================================================================================================================================
TOTAL RETURN (1)..............................    9.41%     2.55%    21.07%     (2.88)%    14.30%    (0.26)%   29.72%     (4.53)%
=================================================================================================================================
RATIOS/SUPPLEMENTAL DATA
Net Assets, End of Year (Millions)............    $687      $460      $346         $71       $88       $44       $24           $9
Ratio of Total Expenses to Average Net
 Assets.......................................    0.20%     0.20%     0.20%      0.18%*     0.20%     0.20%     0.20%      0.18%*
Ratio of Net Investment Income to
 Average Net Assets...........................    6.64%     6.54%     6.55%      6.88%*     6.66%     6.75%     6.90%      7.70%*
Portfolio Turnover Rate.......................      56%       80%       71%        63%        58%       46%       45%        70%
(1) Total return figures do not reflect the annual account maintenance fee of $10.
 * Annualized.
 + Subscription period for the Portfolio was from January 18, 1994, through February 28, 1994, during
   which time all assets were held in money market instruments.
</TABLE>
    
 
- --------------------------------------------------------------------------------
 
YIELD AND
TOTAL RETURN          From time to time each Portfolio may advertise its yield
                      and total return. Both yield and total return figures are
                      based on historical earnings and are not intended to
                      indicate future performance. The "total return" of a
                      Portfolio refers to the average annual compounded rates of
                      return over one-, five- and ten-year periods or for the
                      life of the Portfolio (as stated in the advertisement)
                      that would equate an initial amount invested at the
                      beginning of a stated period to the ending redeemable
                      value of the investment, assuming the reinvestment of all
                      dividend and capital gains distributions.
 
                      In accordance with industry guidelines set forth by the
                      U.S. Securities and Exchange Commission, the "30-day
                      yield" of a Portfolio is calculated by dividing the net
                      investment income per share earned during a 30-day period
                      by the net asset value per share on the last day of the
                      period. Net investment income includes interest and
                      dividend income earned on the Portfolio's securities; it
                      is net of all expenses and all recurring and nonrecurring
                      charges that have been applied to all shareholder
                      accounts. The yield calculation assumes that the net
                      investment income earned over 30 days is compounded
                      monthly for six months and then annualized. Methods used
                      to calculate advertised yields are standardized for all
                      stock and bond mutual funds. However, these methods differ
                      from the accounting methods used by a Portfolio to
                      maintain its books and records, and so the advertised
                      30-day yield may not fully reflect the income paid to an
                      investor's account.
- --------------------------------------------------------------------------------
 
                                        8
<PAGE>   11
 
INVESTMENT
OBJECTIVE

EACH PORTFOLIO
SEEKS TO MATCH
THE INVESTMENT
PERFORMANCE OF ITS
RESPECTIVE INDEX      The Fund is an open-end diversified investment company
                      designed as an "index" fund. The Fund consists of four
                      Portfolios, each of which seeks to match the investment
                      results of a particular investment grade bond index
                      through the use of index sampling techniques. The Total
                      Bond Market Portfolio seeks to replicate the performance
                      of a broad market-weighted bond index, while the
                      Short-Term Bond, Intermediate-Term Bond and Long-Term
                      Bond Portfolios attempt to replicate the performance of
                      market-weighted bond indexes with prescribed maturity
                      standards. There is no assurance that any of the Fund's
                      Portfolios will achieve its stated objective.
 
                      The investment objective of each Portfolio is fundamental
                      and so cannot be changed without the approval of a
                      majority of a Portfolio's shareholders.
- --------------------------------------------------------------------------------
 
INVESTMENT
POLICIES

EACH PORTFOLIO USES A
"PASSIVE" APPROACH
TO INVEST IN FIXED-
INCOME SECURITIES     The four Portfolios of the Fund are not managed according
                      to traditional methods of "active" investment management,
                      which involve the buying and selling of securities based
                      upon economic, financial, and market analyses and
                      investment judgment. Instead, the Portfolios, utilizing a
                      "passive" or "indexing" investment approach, will attempt
                      to duplicate the investment performance of their
                      respective indexes through statistical sampling
                      procedures. Each Portfolio will invest in a group of
                      fixed-income securities selected from its respective index
                      which, when taken together, are expected to perform
                      similarly to the index as a whole. This sampling technique
                      is expected to enable each Portfolio to track the dividend
                      income and price movements of its respective index, while
                      minimizing brokerage, custodial and accounting costs. The
                      Portfolios are managed without regard to tax
                      ramifications.
 
                      The TOTAL BOND MARKET PORTFOLIO will invest in a portfolio
                      of fixed-income securities selected to match the Lehman
                      Brothers Aggregate Bond Index (the "Aggregate Bond
                      Index"). The Aggregate Bond Index is a broad
                      market-weighted index which encompasses four major classes
                      of investment grade fixed-income securities in the United
                      States: U.S. Treasury and agency securities, corporate
                      bonds, international (dollar-denominated) bonds, and
                      mortgage-backed securities, with maturities greater than
                      one year.
 
                      The SHORT-TERM BOND PORTFOLIO will invest in a portfolio
                      of fixed-income securities selected to match the Lehman
                      Brothers Mutual Fund Short (1-5) Government/ Corporate
                      Index (the "Short-Term Index"). The Short-Term Index is a
                      market-weighted index which encompasses three major
                      classes of investment grade fixed-income securities: U.S.
                      Treasury and agency securities, corporate bonds, and
                      international (dollar-denominated) bonds, all with
                      maturities between 1 and 5 years.
 
                      The INTERMEDIATE-TERM BOND PORTFOLIO will invest in a
                      portfolio of fixed-income securities selected to match the
                      Lehman Brothers Mutual Fund Intermediate (5-10)
                      Government/Corporate Index (the "Intermediate-Term
                      Index"). The Intermediate-Term Index is a market-weighted
                      index which encompasses three major classes of investment
                      grade fixed-income securities: U.S. Treasury and agency
                      securities, corporate bonds, and international
                      (dollar-denominated) bonds, all with maturities between 5
                      and 10 years.
 
                                        9
<PAGE>   12
 
                      The LONG-TERM BOND PORTFOLIO will invest in a portfolio of
                      fixed-income securities selected to match the Lehman
                      Brothers Long (10+) Government/Corporate Index (the
                      "Long-Term Index"). The Long-Term Index is a market-
                      weighted index which encompasses three major classes of
                      investment grade fixed-income securities: U.S. Treasury
                      and agency securities, corporate bonds, and international
                      (dollar-denominated) bonds, all with maturities greater
                      than 10 years.
                      Each Portfolio will invest 80% or more of its assets in
                      securities included in its respective index. As of
                      December 31, 1997, the major classes of fixed-income
                      securities represented the following proportions of the
                      respective indexes total market values:

<TABLE>
<CAPTION>
                                                            BOND INDEX     INDEX       TERM INDEX       INDEX
                                                            ----------   ----------   -------------   ---------
                               <S>                          <C>          <C>          <C>             <C>
                               U.S. Treasury and
                                 agency securities               49%          83%            58%           65%
                               Corporate bonds                   17%          14%            32%           29%
                               International (dollar-
                                 denominated) bonds               4%           3%            10%            6%
                               Mortgage-backed securities        30%           0%             0%            0%
                               Dollar-weighted average
                                 maturity (Years)            8.7 yrs      2.7 yrs        7.4 yrs      23.6 yrs

</TABLE>
 
                      The Portfolios of the Fund may, from time to time,
                      substitute one type of investment grade bond for another.
                      For instance, a Portfolio may hold more short-term
                      corporate bonds (fewer short-term U.S. Treasury bonds)
                      than represented in the Index so as to increase income.
                      This corporate substitution strategy will entail the
                      assumption of additional credit risk; however, substantial
                      diversification within the corporate sector should
                      moderate issue-specific credit risk. In addition, current
                      investment policy restricts corporate substitutions to
                      issues with less than 4 years remaining to maturity and in
                      aggregate no more than 15% of net assets. Overall, credit
                      risk is expected to be very low for each of the
                      Portfolios.
 
                      Fixed-income securities will be primarily of investment
                      grade quality -- i.e., those rated at least Baa3 by
                      Moody's Investors Service, Inc. or BBB- by Standard &
                      Poor's Corporation. Securities rated Baa or BBB are
                      considered as medium grade obligations. Interest payments
                      and principal are regarded as adequate for the present but
                      certain protective elements found in higher rated bonds
                      may be lacking. Such bonds lack outstanding investment
                      characteristics and, in fact, have speculative
                      characteristics as well.
 
                      In its effort to duplicate the investment performance of
                      its Index, each Portfolio will invest in fixed-income
                      securities approximating its relative proportion of the
                      Index's total market value. For the Total Bond Market
                      Portfolio, these investments will include U.S. Treasury
                      and agency securities, mortgage-backed securities, and
                      corporate and international (dollar-denominated) bonds.
                      For the Short-Term Bond, Intermediate-Term Bond and
                      Long-Term Bond Portfolios, these investments include U.S.
                      Treasury and agency securities, corporate debt and
                      international (dollar-
 
                                       10
<PAGE>   13
 
                      denominated) debt. The Portfolios may invest in U.S.
                      Treasury bills, notes and bonds and other "full faith and
                      credit" obligations of the U.S. Government. The Portfolios
                      may also invest in U.S. Government agency securities,
                      which are debt obligations issued or guaranteed by
                      agencies or instrumentalities of the U.S. Government. Such
                      "agency" securities may not be backed by the "full faith
                      and credit" of the U.S. Government. Such U.S. Government
                      agencies may include the Federal Farm Credit Banks, the
                      Resolution Trust Corporation and in the case of the Total
                      Bond Market Portfolio, the Government National Mortgage
                      Association. Even though they all carry top (AAA) credit
                      ratings, "agency" obligations are not explicitly
                      guaranteed by the U.S. Government and so are perceived as
                      somewhat riskier than comparable Treasury bonds.
 
                      Each Portfolio may also invest up to 20% of its assets in
                      short-term money market instruments, and may invest in
                      bond (interest rate) futures contracts and options to a
                      limited extent. Such securities will be held only to
                      invest uncommitted cash balances, to maintain liquidity to
                      meet shareholder redemptions, or to minimize trading
                      costs. The Portfolios will not invest in such securities
                      as part of a temporary defensive strategy (such as
                      altering the aggregate maturity of a Portfolio) to protect
                      the Fund against potential bond market declines. Each
                      Portfolio intends to remain fully invested, to the extent
                      practicable, in a pool of securities which will duplicate
                      the investment characteristics of the respective index.
                      See "Implementation of Policies" for a description of
                      other investment practices of the Fund.
 
                      The Fund is responsible for voting the shares of all
                      securities it holds.
 
                      These investment policies are not fundamental and so may
                      be changed by the Board of Directors without shareholder
                      approval. However, shareholders would be notified prior to
                      any material change.
- --------------------------------------------------------------------------------
 
INVESTMENT
RISKS                 As mutual funds investing primarily in fixed-income
                      securities, the Portfolios are subject to interest rate,
                      income, call and credit risks. Since the Total Bond Market
                      Portfolio also invests in mortgage-backed securities, the
                      Portfolio is also subject to prepayment risk.
 
THE PORTFOLIOS ARE
SUBJECT TO INTEREST
RATE RISK             INTEREST RATE RISK is the potential for fluctuations in
                      bond prices due to changing interest rates. As a rule,
                      bond prices vary inversely with interest rates. If
                      interest rates rise, bond prices generally decline; if
                      interest rates fall, bond prices generally rise. In
                      addition, for a given change in interest rates,
                      longer-maturity bonds fluctuate more in price than
                      shorter-maturity bonds. To compensate investors for these
                      larger fluctuations, longer-maturity bonds usually offer
                      higher yields than shorter-maturity bonds, other factors,
                      including credit quality, being equal.
 
                      These basic principles of bond prices also apply to U.S.
                      Government securities. A security backed by the "full
                      faith and credit" of the U.S. Government is guaranteed
                      only as to its stated interest rate and face value at
                      maturity, not its current market price. Just like other
                      fixed-income securities, government-guaranteed securities
                      will fluctuate in value when interest rates change.
 
                                       11
<PAGE>   14
 
                      The TOTAL BOND MARKET and INTERMEDIATE-TERM BOND
                      PORTFOLIOS maintain an intermediate-term dollar-weighted
                      average maturity, and are therefore subject to a moderate
                      to high level of interest rate risk. Interest rate risk
                      for the SHORT-TERM BOND PORTFOLIO should be modest.
                      Because of the short-term dollar-weighted average
                      maturities, the Portfolio is expected to exhibit low to
                      moderate price fluctuations as interest rates change. The
                      LONG-TERM BOND PORTFOLIO is exposed to substantial
                      interest rate risk. The Portfolio is expected to have a
                      dollar-weighted average maturity in excess of 15 years
                      which exposes it to high to very high price fluctuations
                      due to changing interest rates.
 
                      As an illustration of interest rate risk, the chart below
                      depicts the effect of a two percentage point change in
                      interest rates on three bonds of varying maturities:
 
                        PERCENTAGE CHANGE IN PRICE OF A PAR BOND YIELDING 7.5%
 
                      ----------------------------------------------------------
<TABLE>
<CAPTION>
                                                             2 PERCENTAGE POINT   2 PERCENTAGE POINT
                                                                INCREASE IN          DECREASE IN
                                     STATED MATURITY           INTEREST RATES       INTEREST RATES
                               ----------------------------  ------------------   ------------------
                               <S>                           <C>                  <C>
                               Short-Term (2.5 years)              - 4.4%               + 4.6%
                               Intermediate-Term (10 years)        -12.7%               +15.2%
                               Long-Term (20 years)                -17.8%               +24.1%
</TABLE>
 
                      This chart is intended to provide you with guidelines for
                      determining the degree of interest rate risk you may be
                      willing to assume. The yield and price changes shown
                      should not be taken as representative of a Portfolio's
                      current or future yield or expected changes in a
                      Portfolio's share price.
 
THE PORTFOLIOS ARE
SUBJECT TO            INCOME RISK is the potential for a decline in a
INCOME RISK           Portfolio's income due to falling market interest rates.
                      In relative terms, income risk will be higher for the
                      Fund's shorter-term Portfolios and lower for the Fund's
                      longer-term Portfolios.
 
THE LONG-TERM BOND
PORTFOLIO IS SUBJECT
TO CALL RISK          An additional risk associated with long-term corporate
                      bonds is call risk. CALL RISK is the possibility that
                      corporate bonds held by the Portfolio will be repaid prior
                      to maturity. Call provisions, common in many corporate
                      bonds, allow bond issuers to redeem bonds prior to
                      maturity (at a specific price). When interest rates are
                      falling, bond issuers often exercise these call
                      provisions, paying off bonds that carry high stated
                      interest rates and often issuing new bonds at lower rates.
                      For the Portfolio, the result would be that bonds with
                      high interest rates are "called" and must be replaced with
                      lower-yielding instruments. In these circumstances, the
                      income of the Portfolio would decline. Reflecting these
                      additional credit and call risks, the corporate portion of
                      the portfolio will generally offer higher yields than the
                      government portion.
 
THE TOTAL BOND
MARKET PORTFOLIO
IS SUBJECT TO
PREPAYMENT RISK       As a mutual fund investing a portion of its assets in
                      mortgage-backed securities (see chart on page 10), the
                      Total Bond Market Portfolio is subject to prepayment risk
                      to a limited extent. PREPAYMENT RISK is the possibility
                      that, during periods of declining interest rates, the
                      principal invested in high-yielding mortgage-backed
                      securities
 
                                       12
<PAGE>   15
 
                      will be repaid earlier than scheduled, and the Fund will
                      be forced to reinvest the unanticipated payments at
                      generally lower interest rates.
 
                      Prepayment risk has two important effects on the
                      Portfolio. First, when interest rates fall and principal
                      prepayments are reinvested at lower interest rates, the
                      income that the Portfolio derives from mortgage-backed
                      securities is reduced. Second, like other fixed-income
                      securities, mortgage-backed securities generally decline
                      in price when interest rates rise. However, because of
                      prepayment risk, mortgage-backed securities (and thus in
                      part the share price of the Portfolio and the value of the
                      Index) will not enjoy as large a gain in market value as
                      ordinary bonds when interest rates fall. In part to
                      compensate for prepayment risk, mortgage-backed securities
                      generally offer higher yields than bonds of comparable
                      credit quality and maturity.
 
CREDIT RISK IS          
EXPECTED TO BE LOW    CREDIT RISK is the possibility that an issuer of
                      securities held by a Portfolio will be unable to make
                      payments of either interest or principal. The credit risk
                      of a Portfolio is a function of the credit quality of its
                      underlying securities.
                      The credit quality of each Portfolio is expected to be
                      very high, and thus credit risk should be low. As of
                      December 31, 1997, the average quality, as rated by
                      Moody's Investors Service, Inc., of each Portfolio's
                      benchmark index was as follows:
<TABLE>
                                          <S>                                                <C>
                                          Aggregate Bond Index.............................  Aaa
                                          Short-Term Bond Index............................  Aaa
                                          Intermediate-Term Bond Index.....................  Aa1
                                          Long-Term Bond Index.............................  Aa2
</TABLE>
 
                      To a limited extent, the Portfolios are also exposed to
                      EVENT RISK, the possibility that corporate fixed-income
                      securities held by the Portfolios may suffer a substantial
                      decline in credit quality and market value due to a
                      corporate restructuring. Corporate restructurings, such as
                      mergers, leveraged buyouts, takeovers or similar events,
                      are often financed by a significant expansion of corporate
                      debt. As a result of the added debt burden, the credit
                      quality and market value of a firm's existing debt
                      securities may decline significantly. While event risk may
                      be high for certain corporate and international
                      (dollar-denominated) securities held by the Portfolios,
                      event risk for each Portfolio in the aggregate should be
                      low because of each Portfolio's diversified holdings and
                      the small percentage of Portfolio assets invested in these
                      securities.
 
                      The corporate substitution strategy will increase credit
                      risk somewhat, as short-term investment grade corporate
                      bonds are substituted for U.S. Treasury bonds and notes;
                      however, owing to the diversified nature of the
                      Portfolios, and policies limiting the maturity and maximum
                      amount of substitutions, the overall credit and event risk
                      of the Portfolios is expected to be low.
 
NO CURRENCY RISK
IN ANY PORTFOLIO      While each of the chosen Lehman Index benchmarks do have
                      limited exposure to international bonds, there is no
                      currency risk associated with the investments since they
                      are all dollar-denominated.
- --------------------------------------------------------------------------------
 
                                       13
<PAGE>   16
 
WHO SHOULD
INVEST
INVESTORS SEEKING TO
PARTICIPATE IN THE
"BOND MARKET" AS A
WHOLE OR ITS VARIOUS
MATURITY SEGMENTS     The Portfolios are designed for individual and
                      institutional investors seeking well-diversified, low-cost
                      ways to participate in the U.S. fixed-income markets. The
                      Portfolios will be essentially fully invested at all
                      times. Because the Total Bond Market Portfolio will
                      represent all major sectors of the investment grade fixed-
                      income securities market, the Portfolio is a suitable
                      vehicle for those investors seeking ownership in the "bond
                      market" as a whole, without regard to particular sectors.
                      The Short-Term Bond, Intermediate-Term Bond and Long-Term
                      Bond Portfolios are suitable vehicles for those investors
                      seeking ownership in specific maturity segments of the
                      "bond market." Each Portfolio concentrates on bonds of
                      various maturities as illustrated in the chart on page 10.
                      Because of the risks associated with bond investments,
                      each Portfolio is intended to be a long-term investment
                      vehicle and is not designed to provide investors with a
                      means of speculating on short-term bond market movements.
 
   
                      As with all longer-term, fixed-income investments, the
                      share price of the Total Bond Market, Intermediate-Term
                      Bond and Long-Term Bond Portfolios will vary, with the
                      Long-Term Bond Portfolio expected to exhibit the greatest
                      volatility. Share price volatility should be significantly
                      less for the Short-Term Bond Portfolio. Credit risk should
                      be minimal for each Portfolio. The investment risks are
                      described on pages 11 through 13.
    
 
                      The Portfolios are also suitable for those investors with
                      common stock holdings who are seeking a complementary
                      fixed-income investment to create a more balanced asset
                      mix. Because of potential share price fluctuations, the
                      Portfolios may be inappropriate for investors who have
                      short-term objectives or who require stability of
                      principal.
- --------------------------------------------------------------------------------
 
IMPLEMENTATION
OF POLICIES           The Portfolios follow a variety of investment practices in
                      an effort to duplicate the total return of their
                      respective indexes.
 
THE PORTFOLIOS INVEST
IN FIXED-INCOME
SECURITIES            Each Portfolio will invest at least 80% or more of its
                      assets in securities included in its benchmark index. The
                      indexes measure the total investment return (capital
                      change plus income) provided by a universe of fixed-income
                      securities, weighted by the market value outstanding of
                      each security. The securities included in each index
                      generally meet the following criteria, as defined by
                      Lehman Brothers: an outstanding market value of at least
                      $100 million; and investment grade quality -- i.e., rated
                      a minimum of Baa3 by Moody's Investors Service, Inc. The
                      maturities of securities included in each index will vary
                      as described on page 10. If a security held in the Fund's
                      portfolio is downgraded to a rating below these minimum
                      standards, the Fund may continue to hold it until such
                      time as the adviser deems it most advantageous to dispose
                      of the security.
 
THE PORTFOLIOS USE A
"SAMPLING" TECHNIQUE  The Portfolios will be unable to hold all of the
                      individual issues which comprise the indexes because of
                      the large number of securities involved. Instead, each
                      Portfolio will hold a representative sample of the
                      securities in its respective index, selecting a few issues
                      to represent entire "classes" or types of securities in
                      the index. Each Portfolio will be constructed so as to
                      approximately match the composition of its benchmark index
                      as described on pages 9 and 10 after adjusting for the
                      corporate
                                       14
<PAGE>   17
 
                      substitution policy described on page 10. The corporate
                      substitution strategy only applies to the Total Bond
                      Market Portfolio and the Short-Term Bond Portfolio.
 
                      At the broadest level, and adjusted for the corporate
                      substitution strategy, each Portfolio will seek to hold
                      securities which reflect the weighting of the major asset
                      classes in its respective index. For the Total Bond Market
                      Portfolio, these classes include U.S. Treasury and agency
                      securities, corporate bonds, and mortgage-backed
                      securities. For the Short-Term Bond, Intermediate-Term
                      Bond and Long-Term Bond Portfolios, the two major classes
                      of securities include U.S. Treasury and agency securities
                      and corporate bonds. For example, if U.S. Treasury and
                      agency securities represent approximately 60% of an
                      index's interest rate risk, then approximately 60% of the
                      respective Portfolio's interest rate risk will come from
                      such securities. Similarly, if corporate bonds represent
                      20% of the interest rate risk of an index, then they will
                      represent approximately 20% of the interest rate risk of
                      the Portfolio.
 
                      Such a sampling technique is expected to be an effective
                      means of substantially duplicating the income and capital
                      returns provided by each index. Over time, the correlation
                      between the performance of a Portfolio and its respective
                      index is expected to be 0.95 or higher. A correlation of
                      1.00 would indicate perfect correlation, which would be
                      achieved when the net asset value of a Portfolio,
                      including the value of its dividend and capital gain
                      distributions, increases or decreases in exact proportion
                      to changes in the index. The performance and structure of
                      a Portfolio versus that of its respective index is
                      monitored regularly. If significant structural mismatches
                      develop, the Portfolio is rebalanced to bring it in line
                      with the index.
 
THE TOTAL BOND
MARKET PORTFOLIO
MAY INVEST IN
MORTGAGE-BACKED
SECURITIES            As part of its effort to duplicate the investment
                      performance of its Index, the Total Bond Market Portfolio
                      may invest in mortgage-backed securities. Mortgage-backed
                      securities represent an interest in an underlying pool of
                      mortgages. Unlike ordinary fixed-income securities, which
                      generally pay a fixed rate of interest and return
                      principal upon maturity, mortgage-backed securities repay
                      both interest income and principal as part of their
                      periodic payments. Because the mortgages underlying
                      mortgage-backed certificates can be prepaid at any time by
                      homeowners or corporate borrowers, mortgage-backed
                      securities give rise to certain unique "prepayment" risks.
                      See "Investment Risks."
 
                      The Total Bond Market Portfolio may purchase
                      mortgage-backed securities issued by the Government
                      National Mortgage Association (GNMA), the Federal Home
                      Loan Mortgage Corporation (FHLMC), the Federal National
                      Mortgage Association (FNMA), and the Federal Housing
                      Authority (FHA). GNMA securities are guaranteed by the
                      U.S. Government as to the timely payment of principal and
                      interest; securities from other Government-sponsored
                      entities are generally not secured by an explicit pledge
                      of the U.S. Government. The Portfolio may also invest in
                      conventional mortgage securities, which are packaged by
                      private corporations and are not guaranteed by the U.S.
                      Government. Mortgage securities that are guaranteed by the
                      U.S. Government are guaranteed only as to the timely
                      payment of principal and interest. The market values of
                      the securities are not guaranteed and may fluctuate.
 
                                       15
<PAGE>   18
 
EACH PORTFOLIO MAY
INVEST IN SHORT-TERM
MONEY MARKET
INSTRUMENTS           Although they normally seek to remain substantially fully
                      invested in securities in the respective indexes, the
                      Portfolios may invest temporarily in certain short-term
                      money market instruments. Such securities may be used to
                      invest uncommitted cash balances or to maintain liquidity
                      to meet shareholder redemptions. These securities include:
                      obligations of the United States Government and its
                      agencies or instrumentalities; commercial paper, bank
                      certificates of deposit, and bankers' acceptances; and
                      repurchase agreements collateralized by these securities.
 
EACH PORTFOLIO MAY
LEND ITS SECURITIES   Each Portfolio may lend its investment securities to
                      qualified institutional investors for either short-term or
                      long-term purposes of realizing additional income. Loans
                      of securities by a Portfolio will be collateralized by
                      cash, letters of credit, or securities issued or
                      guaranteed by the U.S. Government or its agencies. The
                      collateral will equal at least 100% of the current market
                      value of the loaned securities.
 
PORTFOLIO TURNOVER
IS NOT EXPECTED
TO EXCEED 50%         Although it generally seeks to invest for the long term,
                      each Portfolio retains the right to sell securities
                      irrespective of how long they have been held. It is
                      anticipated that the annual portfolio turnover of each
                      Portfolio will not exceed 50%. A turnover rate of 50%
                      would occur, for example, if one half of the securities of
                      a Portfolio were replaced within one year. A portfolio
                      turnover rate of 100% may be considered high for a bond
                      index fund and would result in additional expenses.
 
DERIVATIVE
INVESTING
                      Derivatives are instruments whose values are linked to or
                      derived from an underlying security or index. The most
                      common and conventional types of derivative securities are
                      futures and options.
 
EACH PORTFOLIO MAY
INVEST IN DERIVATIVE
SECURITIES
                      Each Portfolio may invest in futures contracts and
                      options, but only to a limited extent. Specifically, a
                      Portfolio of the Fund may enter into futures contracts
                      provided that not more than 5% of its assets are required
                      as a futures contract deposit; in addition, a Portfolio
                      may enter into futures contracts and options transactions
                      only to the extent that obligations under such contracts
                      or transactions represent not more than 20% of the
                      Portfolio's assets.
 
                      Futures contracts and options may be used for several
                      common fund management strategies: to maintain cash
                      reserves while simulating full investment, to facilitate
                      trading, to reduce transaction costs, or to seek higher
                      investment returns when a specific futures contract is
                      priced more attractively than other futures contracts or
                      the underlying security or index.
 
                      The Portfolios may use futures contracts for bona fide
                      "hedging" purposes. In executing a hedge, a manager sells,
                      for example, stock index futures to protect against a
                      decline in the stock market. As such, if the market drops,
                      the value of the futures position will rise, thereby
                      offsetting the decline in value of the Portfolios' stock
                      holdings.
 
                      The Fund may also invest in other conventional derivatives
                      designed to replicate the risk/return characteristics of a
                      conventional fixed income note or bond. Such derivatives
                      would be managed, in both structure and concentration, to
                      adhere to the Fund's investment policy restrictions as to
                      market and credit risk.
 
                                       16
<PAGE>   19
 
EACH PORTFOLIO MAY
INVEST IN CMOS        The Portfolios may invest in a relatively conservative
                      class of collateralized mortgage obligations (CMOs) which
                      feature a high degree of cash flow predictability and less
                      vulnerability to mortgage prepayment risk. To reduce
                      credit risk, Vanguard purchases these less risky classes
                      of collateralized mortgage obligations issued only by
                      agencies of the U.S. Government or privately-issued
                      collateralized mortgage obligations that carry
                      high-quality investment-grade ratings.
 
FUTURES CONTRACTS
AND OPTIONS POSE
CERTAIN RISKS
                      The primary risks associated with the use of futures
                      contracts and options are: (i) imperfect correlation
                      between the change in market value of the bonds held by a
                      Portfolio and the prices of futures contracts and options;
                      and (ii) possible lack of a liquid secondary market for a
                      futures contract and the resulting inability to close a
                      futures position prior to its maturity date. The risk of
                      imperfect correlation will be minimized by investing in
                      those contracts whose price fluctuations are expected to
                      resemble those of the Portfolio's underlying securities.
                      The risk that a Portfolio will be unable to close out a
                      futures position will be minimized by entering into such
                      transactions on a national exchange with an active and
                      liquid secondary market.
 
                      The risk of loss in trading futures contracts in some
                      strategies can be substantial, due both to the low margin
                      deposits required and the extremely high degree of
                      leverage involved in futures pricing. As a result, a
                      relatively small price movement in a futures contract may
                      result in immediate and substantial loss (or gain) to the
                      investor. When investing in futures contracts, a Portfolio
                      will segregate cash or other liquid portfolio securities
                      in the amount of the underlying obligation.
- --------------------------------------------------------------------------------
 
   
INVESTMENT
LIMITATIONS
EACH PORTFOLIO HAS
ADOPTED CERTAIN
FUNDAMENTAL
LIMITATIONS           Each Portfolio has adopted limitations on some of its
                      investment policies. Some of these limitations are that
                      each Portfolio will not:
    
 
                      (a) invest more than 5% of its assets in the securities of
                          any single issuer except obligations of the United
                          States Government or government agencies;
                      (b) purchase more than 5% of the voting securities of any
                          issuer;
                      (c) borrow money, except that each Portfolio may borrow
                          from banks (or through reverse repurchase agreements),
                          for temporary or emergency (not leveraging) purposes,
                          including the meeting of redemption requests which
                          might otherwise require the untimely disposition of
                          securities, in an amount not exceeding 15% of the
                          value of a Portfolio's net assets (including the
                          amount borrowed and the value of any outstanding
                          reverse repurchase agreements) at the time the
                          borrowing is made. Whenever borrowings exceed 5% of
                          the value of a Portfolio's net assets, the Portfolio
                          will not make any additional investments;
                      (d) pledge, mortgage or hypothecate its assets to an
                          extent greater than 5% of the value of its total
                          assets; and
                      (e) invest more than 25% of its assets in any one
                          industry.
 
                      A complete list of each Portfolio's investment limitations
                      can be found in the Statement of Additional Information.
                      These limitations are fundamental and may be changed only
                      by approval of a majority of the Portfolio's shareholders.
- --------------------------------------------------------------------------------
 
                                       17
<PAGE>   20
 
   
MANAGEMENT
OF THE FUND
VANGUARD ADMINISTERS
AND DISTRIBUTES
THE FUND              The Fund is a member of The Vanguard Group of Investment
                      Companies, a family of more than 30 investment companies
                      with more than 95 distinct portfolios and total assets in
                      excess of $360 billion. Through their jointly-owned
                      subsidiary, The Vanguard Group, Inc. ("Vanguard"), the
                      Fund and the other funds in the Group obtain at cost
                      virtually all of their corporate management,
                      administrative, shareholder accounting and distribution
                      services. Vanguard also provides investment advisory
                      services on an at-cost basis to certain Vanguard funds. As
                      a result of Vanguard's unique corporate structure, the
                      Vanguard funds have costs substantially lower than those
                      of most competing mutual funds. In 1997, the average
                      expense ratio (annual costs including advisory fees
                      divided by total net assets) for the Vanguard funds
                      amounted to approximately .28% compared to an average of
                      1.24% for the mutual fund industry (data provided by
                      Lipper Analytical Services).
    
 
                      The Officers of the Fund manage its day-to-day operations
                      and are responsible to the Fund's Board of Directors. The
                      Directors set broad policies for the Fund and choose its
                      Officers. A list of the Directors and Officers of the Fund
                      and a statement of their present positions and principal
                      occupations during the past five years can be found in the
                      Statement of Additional Information.
 
                      Vanguard employs a supporting staff of management and
                      administrative personnel needed to provide the requisite
                      services to the funds and also furnishes the funds with
                      necessary office space, furnishings and equipment. Each
                      fund pays its share of Vanguard's net expenses, which are
                      allocated among the funds under methods approved by the
                      Board of Directors (Trustees) of each fund. In addition,
                      each fund bears its own direct expenses, such as legal,
                      auditing and custodian fees.
 
                      Vanguard also provides distribution and marketing services
                      to the Vanguard funds. The funds are available on a
                      no-load basis (i.e., there are no sales commissions or
                      12b-1 fees). However, each fund bears its share of the
                      Group's distribution costs.
- --------------------------------------------------------------------------------
 
   
INVESTMENT
ADVISER
VANGUARD MANAGES
THE FUND'S
INVESTMENTS           Each Portfolio receives all investment advisory services
                      from Vanguard's Fixed Income Group. The Fixed Income Group
                      provides investment advisory services to more than 40
                      Vanguard money market and bond portfolios, both taxable
                      and tax-exempt. Total assets under management by
                      Vanguard's Fixed Income Group were more than $100 billion
                      as of December 31, 1997. The Portfolios are not actively
                      managed, but are instead administered by the Fixed Income
                      Group using computerized, quantitative techniques. The
                      Fixed Income Group is supervised by the Officers of the
                      Fund. Ian A. MacKinnon, Managing Director of Vanguard, has
                      been in charge of the Group since its inception in 1981.
    
 
                      Mr. MacKinnon is responsible for setting the broad
                      investment strategies employed by the Fund, and for
                      overseeing the portfolio manager who implements those
                      strategies on a day-to-day basis.
 
                      The Fund's portfolio manager is Kenneth E. Volpert, a
                      Principal of Vanguard, who also serves as portfolio
                      manager of the Vanguard Variable Insurance
                      Fund -- High-Grade Bond Portfolio and the bond portion of
                      the Vanguard Balanced Index Fund. Mr. Volpert began
                      managing the Vanguard Bond Index Fund in December 1992.
 
                                       18
<PAGE>   21
 
                      For six years prior to joining Vanguard, Mr. Volpert was
                      associated with Mellon Bond Associates.
 
                      The Fixed Income Group places all orders for purchases and
                      sales of portfolio securities. Purchases of portfolio
                      securities are made either directly from the issuer or
                      from securities dealers. The Fixed Income Group may sell
                      portfolio securities prior to their maturity if
                      circumstances and considerations warrant, and if it
                      believes such dispositions advisable. The Group seeks to
                      obtain the best available net price and most favorable
                      execution for all portfolio transactions. When the
                      Portfolio purchases a newly issued security at a fixed
                      price, the Group may designate certain members of the
                      underwriting syndicate to receive compensation associated
                      with that transaction. Certain dealers have agreed to
                      rebate a portion of such compensation directly to the
                      Portfolio to offset their management expenses.
- --------------------------------------------------------------------------------
 
PERFORMANCE
RECORD                The tables in this section provide investment results for
                      the Total Bond Market, Short-Term Bond, Intermediate-Term
                      Bond and Long-Term Bond Portfolios for several periods
                      throughout the Fund's lifetime. The results shown
                      represent "total return" investment performance, which
                      assumes the reinvestment of all capital gains and income
                      dividends for the indicated periods. Also included is
                      comparative information with respect to the unmanaged
                      Aggregate Bond Index described on page 9, the Consumer
                      Price Index, a statistical measure of changes in the
                      prices of goods and services, the Lehman Mutual Fund
                      Short-Term (1-5) Government/Corporate Bond Index, the
                      Lehman Mutual Fund Intermediate (5-10)
                      Government/Corporate Bond Index, and the Lehman Long (10+)
                      Government/Corporate Bond Index. The table does not make
                      any allowance for federal, state or local income taxes,
                      which shareholders must pay on a current basis.
 
                      The results shown should not be considered a
                      representation of the total return from an investment made
                      in the Portfolio today. This information is provided to
                      help investors better understand the Portfolio and may not
                      provide a basis for comparison with other investments or
                      mutual funds which use a different method to calculate
                      performance.
 
                                   AVERAGE ANNUAL TOTAL RETURN FOR
                       VANGUARD BOND INDEX FUND -- TOTAL BOND MARKET PORTFOLIO
 
<TABLE>
<CAPTION>
                               FISCAL PERIODS     TOTAL BOND      AGGREGATE     CONSUMER
                               ENDED 12/31/97  MARKET PORTFOLIO   BOND INDEX   PRICE INDEX
                               --------------  ----------------   ----------   -----------
                               <S>             <C>                <C>          <C>
                               1 Year                9.44%           9.65%        1.70%
                               3 Years              10.24           10.42         2.52
                               5 Years               7.42            7.48         2.60
                               10 Years              8.88            9.18         3.41
                               Lifetime*             8.09            8.51         3.51
</TABLE>
 
                      * December 11, 1986 to December 31, 1997.
 
                                       19
<PAGE>   22
 
                                   AVERAGE ANNUAL TOTAL RETURN FOR
                        VANGUARD BOND INDEX FUND -- SHORT-TERM BOND PORTFOLIO
<TABLE>
<CAPTION>
                                                                     LEHMAN MUTUAL FUND
                               FISCAL PERIODS     SHORT-TERM      SHORT (1-5) GOVERNMENT/     CONSUMER
                               ENDED 12/31/97   BOND PORTFOLIO      CORPORATE BOND INDEX     PRICE INDEX
                               --------------  ----------------   ------------------------   -----------
                               <S>             <C>                <C>                        <C>
                               1 Year                7.04%                  7.13%               1.70%
                               3 Years               8.10                   8.17                2.52
                               Lifetime*             6.18                   6.28                2.50
</TABLE>
 
                      * March 1, 1994 to December 31, 1997.
 
                                   AVERAGE ANNUAL TOTAL RETURN FOR
                          VANGUARD BOND INDEX FUND -- INTERMEDIATE-TERM BOND
                                              PORTFOLIO
<TABLE>
<CAPTION>
                                                                        LEHMAN MUTUAL FUND
                                                 INTERMEDIATE-         INTERMEDIATE (5-10)
                               FISCAL PERIODS        TERM                  GOVERNMENT/              CONSUMER
                               ENDED 12/31/97   BOND PORTFOLIO         CORPORATE BOND INDEX       PRICE INDEX
                               --------------  -----------------   ----------------------------   ------------
                               <S>             <C>                 <C>                            <C>
                               1 Year                 9.41%                     9.43%                 1.70%
                               3 Years               10.75                     10.92                  2.52
                               Lifetime*              7.49                      7.60                  2.50
</TABLE>
 
                      * March 1, 1994 to December 31, 1997.
 
                                   AVERAGE ANNUAL TOTAL RETURN FOR
                         VANGUARD BOND INDEX FUND -- LONG-TERM BOND PORTFOLIO
<TABLE>
<CAPTION>
                                                                         LEHMAN
                               FISCAL PERIODS     LONG-TERM      LONG (10+) GOVERNMENT/      CONSUMER
                               ENDED 12/31/97  BOND PORTFOLIO     CORPORATE BOND INDEX     PRICE INDEX
                               --------------  ---------------   -----------------------   ------------
                               <S>             <C>               <C>                       <C>
                               1 Year               14.30%                14.52%               1.70%
                               3 Years              13.93                 14.22                2.52
                               Lifetime*             9.41                  9.59                2.50
</TABLE>
 
                      * March 1, 1994 to December 31, 1997.
- --------------------------------------------------------------------------------
 
DIVIDENDS,
CAPITAL GAINS
AND TAXES

EACH PORTFOLIO PAYS
MONTHLY DIVIDENDS     Dividends consisting of virtually all of the ordinary
                      income of each Portfolio are declared daily and are
                      payable to shareholders of record at the time of
                      declaration. Such dividends are paid on the first business
                      day of each month. Capital gains distributions, if any,
                      are made annually. In addition, each Portfolio may
                      occasionally be required to make supplemental dividend or
                      capital gains distributions at some other time during the
                      year.
 
                      Each Portfolio's dividend and capital gains distributions
                      may be reinvested in additional shares or received in
                      cash. See "Choosing a Distribution Option" for a
                      description of these distribution methods. Shareholders
                      who choose to reinvest their dividend distributions will
                      receive a quarterly (not monthly) confirmation statement.
 
                      Each Portfolio automatically deducts a $10 annual account
                      maintenance fee from the dividend income of each account
                      on a quarterly basis (at a rate of $2.50 per quarter). If
                      the monthly dividend for the account is less than the fee
                      to be deducted, the Portfolio will redeem sufficient
                      shares to make up the difference. The Board of Directors
                      reserves the right to change the annual account
                      maintenance fee to reflect
 
                                       20
<PAGE>   23
 
                      the actual cost of maintaining smaller shareholder
                      accounts. For federal tax purposes, the account
                      maintenance fee does not reduce dividend income and is
                      treated as an investment expense (deductible as a
                      miscellaneous itemized deduction in the case of individual
                      investors). This fee will be waived for shareholders with
                      an account balance of $10,000 or more at the time of the
                      quarterly deduction.
 
                      Pursuant to the Internal Revenue Code, certain dividend
                      and capital gains distributions declared by each Portfolio
                      during December, if received by shareholders by January
                      31, are deemed to have been paid by the Portfolio and
                      received by shareholders on December 31 of the prior year.
 
                      Each Portfolio intends to continue to qualify for taxation
                      as a "regulated investment company" under the Internal
                      Revenue Code so that it will not be subject to federal
                      income tax to the extent its income is distributed to
                      shareholders. Dividends paid by the Portfolio from net
                      investment income and net short-term capital gains,
                      whether received in cash or reinvested in additional
                      shares, will be taxable to shareholders as ordinary
                      income. For corporate investors, dividends paid by the
                      Portfolios from net investment income will generally not
                      qualify for the intercorporate dividends-received
                      deduction.
 
                      Distributions paid by a Portfolio from long-term capital
                      gains, whether received in cash or reinvested in
                      additional shares, are taxable as long-term capital gains,
                      regardless of the length of time you have owned shares in
                      the Portfolio. Long-term capital gains may be taxed at
                      different rates depending on how long the Fund held the
                      securities. Capital gains distributions are made when a
                      Portfolio realizes net capital gains on sales of portfolio
                      securities during the year. Realized capital gains are not
                      expected to be a significant or predictable part of
                      investment return of each Portfolio.
 
                      The Fund will notify you annually as to the tax status of
                      dividend and capital gains distributions paid by each
                      Portfolio.
 
A CAPITAL GAIN OR LOSS
MAY BE REALIZED
UPON EXCHANGE OR
REDEMPTION            A sale of shares of a Portfolio is a taxable event and may
                      result in a capital gain or loss. A capital gain or loss
                      may be realized from an ordinary redemption of shares, a
                      checkwriting redemption, or an exchange of shares between
                      two mutual funds (or two portfolios of a mutual fund).
 
                      Dividend distributions, capital gains distributions, and
                      capital gains or losses from redemptions and exchanges may
                      be subject to state and local taxes.
 
   
                      Each Portfolio is required to withhold 31% of taxable
                      dividends, capital gains distributions, and redemptions
                      paid to shareholders who have not complied with IRS
                      taxpayer identification regulations. You may avoid this
                      withholding requirement by certifying on your Account
                      Registration Form your proper Social Security or employer
                      identification number and by certifying that you are not
                      subject to backup withholding.
    
 
                      The Fund has obtained a Certificate of Authority to do
                      business as a foreign corporation in Pennsylvania and
                      does business and maintains an office in that
 
                                       21
<PAGE>   24
 
                      state. In the opinion of counsel, the shares of the Fund
                      are exempt from Pennsylvania personal property taxes.
 
                      The tax discussion set forth above is included for
                      general information only. Prospective investors should
                      consult their own tax advisers concerning the tax
                      consequences of an investment in the Fund.
- --------------------------------------------------------------------------------
 
THE SHARE PRICE
OF EACH PORTFOLIO     Each Portfolio's share price, or "net asset value" per
                      share, is calculated by dividing the total assets of the
                      Portfolio, less all liabilities, by the total number of
                      shares outstanding, except for the Total Bond Portfolio
                      whereby net asset value is calculated by dividing the net
                      assets attributed to each share class, by the total number
                      of shares outstanding for that share class. The net asset
                      value is determined as of the close of trading on the New
                      York Stock Exchange (the "Exchange"), generally 4:00 p.m.
                      Eastern time on each day that the Exchange is open for
                      trading.
 
                      Short term instruments (those with remaining maturities of
                      60 days or less) may be valued at cost, plus or minus any
                      amortized discount or premium, which approximates market
                      value.
 
                      Bonds and other fixed income securities may be valued on
                      the basis of prices provided by a pricing service when
                      such prices are believed to reflect the fair market value
                      of such securities. The prices provided by a pricing
                      service may be determined without regard to bid or last
                      sale prices of each security, but take into account
                      institutional-size transactions in similar groups of
                      securities as well as any developments related to specific
                      securities.
 
                      Other assets and securities for which no quotations are
                      readily available or which are restricted as to sale (or
                      resale) are valued by such methods as the Board of
                      Directors deems in good faith to reflect fair value.
 
   
                      The share price for each Portfolio of the Fund can be
                      found daily in the mutual fund listings of most major
                      newspapers under the heading of Vanguard Index Funds.
    
- --------------------------------------------------------------------------------
 
GENERAL
INFORMATION           The Fund is a Maryland corporation. The Articles of
                      Incorporation permit the Directors to issue 2,000,000,000
                      shares of common stock, with a $.001 par value. The Board
                      of Directors has the power to designate one or more
                      portfolios and classes of shares of common stock of such
                      portfolios and to classify or reclassify any unissued
                      shares with respect to such portfolios and classes.
                      Currently the Fund is offering shares of four series. The
                      Total Bond Market Portfolio offers two separate classes of
                      shares: the Total Bond Market Portfolio Investor Shares,
                      which is open to investors with a minimum investment of
                      $3,000, and the Total Bond Market Portfolio Institutional
                      Shares which are designed for investors who meet certain
                      administrative criteria and a minimum initial investment
                      of $10 million.
 
                      The shares of each Portfolio are fully paid and
                      non-assessable; have no preference as to conversion,
                      exchange, dividends, retirement or other features; and
                      have no pre-emptive rights. Such shares have
                      non-cumulative voting rights, meaning that
 
                                       22
<PAGE>   25
 
                      the holders of more than 50% of the shares voting for the
                      election of Directors can elect 100% of the Directors if
                      they so choose.
 
                      Annual meetings of shareholders will not be held except as
                      required by the Investment Company Act of 1940 and other
                      applicable law. An annual meeting will be held to vote on
                      the removal of a Director or Directors of the Fund if
                      requested in writing by the holders of not less than 10%
                      of the outstanding shares of the Fund.
 
                      All securities and cash for the Total Bond Market
                      Portfolio are held by Chase Manhattan Bank, New York, NY.
                      All securities and cash for the Short-Term Bond,
                      Intermediate-Term Bond and Long-Term Bond Portfolios are
                      held by State Street Bank and Trust Company, Boston, MA.
                      CoreStates Bank, N.A., Philadelphia, PA, holds daily cash
                      balances that are used by the Fund's Portfolios to invest
                      in repurchase agreements or securities acquired in these
                      transactions. The Vanguard Group, Inc., Valley Forge, PA,
                      serves as the Fund's Transfer and Dividend Disbursing
                      Agent. Price Waterhouse LLP, serves as independent
                      accountants for the Fund and will audit its financial
                      statements annually. The Fund is not involved in any
                      litigation.
- --------------------------------------------------------------------------------
 
                                       23
<PAGE>   26
 
                               SHAREHOLDER GUIDE
 
OPENING AN
ACCOUNT AND
PURCHASING
SHARES                You may open a regular (non-retirement) account, either by
                      mail or wire. Simply complete and return an Account
                      Registration Form and any required legal documentation,
                      indicating the Portfolio you have chosen and amount you
                      wish to invest. Your purchase must be equal to or greater
                      than the $3,000 minimum initial investment requirement in
                      any Portfolio ($1,000 for Uniform Gifts/Transfers to
                      Minors Act accounts; $500 minimum for an Education IRA).
                      You must open a new Individual Retirement Account by mail
                      (IRAs may not be opened by wire) using a Vanguard IRA
                      Adoption Agreement. Your purchase must be equal to or
                      greater than the $1,000 minimum initial investment
                      requirement, but no more than $2,000 if you are making a
                      regular IRA contribution. Rollover contributions are
                      generally limited to the amount withdrawn within the past
                      60 days from an IRA or other qualified retirement plan. If
                      you need assistance with the Account Registration Form or
                      have any questions about the Fund, please call our
                      Investor Information Department (1-800-662-7447). NOTE:
                      For other types of account registrations (e.g.,
                      corporations, associations, other organizations, trusts or
                      powers of attorney), please call us to determine which
                      additional forms you may need.
 
                      Each Portfolio's shares are purchased at the
                      next-determined net asset value after your investment has
                      been received. See "When Your Account Will Be Credited".
                      The Fund is offered on a no-load basis (i.e., there are no
                      sales commissions or 12b-1 fees).
 
PURCHASE
RESTRICTIONS          1) Because of the risks associated with bond investments,
                         each Portfolio is intended to be a long-term investment
                         vehicle and is not designed to provide investors with a
                         means of speculating on short-term bond market
                         movements. Excessive trading results in higher
                         transaction costs paid for by the remaining
                         shareholders. Consequently, the Fund reserves the right
                         to assess a transaction fee (payable to the Portfolio)
                         or to reject any specific purchase (and exchange
                         purchase) request. Shareholders subject to any
                         transaction fee will be notified by the Fund. The Fund
                         also reserves the right to suspend the offering of
                         shares for a period of time.
 
                      2) Vanguard will not accept third-party checks to purchase
                         shares of the Fund. Please be sure your purchase check
                         is made payable to The Vanguard Group.
 
ADDITIONAL
INVESTMENTS           Subsequent investments may be made by mail ($100 minimum
                      per Portfolio), wire ($1,000 minimum), exchange from
                      another Vanguard Fund account ($100 minimum per
                      Portfolio), or Vanguard Fund Express. Subsequent
                      investments to Individual Retirement Accounts may be made
                      by mail ($100 minimum) or exchange from another Vanguard
                      Fund account. In some instances, contributions may be made
                      by wire or Vanguard Fund Express. Please call us for more
                      information on these options.
- --------------------------------------------------------------------------------
 
                                       24
<PAGE>   27
<TABLE>
<S>                             <C>                                         <C>
                                                                            ADDITIONAL INVESTMENTS
                                NEW ACCOUNT                                 TO EXISTING ACCOUNTS
PURCHASING BY MAIL              Please include the amount of                                                
                                your initial investment and the             Additional investments should
Complete and sign the           name of the Portfolios you have             include the Invest-by-Mail
enclosed Account                selected on the registration                remittance form attached to your
Registration Form               form, make your check payable to            Fund confirmation statements.
                                The Vanguard Group (Portfolio               Please make your check payable
                                Number), see below for the                  to The Vanguard Group (Portfolio
                                appropriate number and mail to:             Number), write your account
                                                                            number on your check, and using
                                THE VANGUARD GROUP                          the return envelope provided,
                                P.O. BOX 2600                               mail to the address indicated on
                                VALLEY FORGE, PA 19482-2600                 the Invest-by-Mail Form. See
                                                                            below for the appropriate
For express or                  THE VANGUARD GROUP                          Portfolio number.
registered mail,                455 DEVON PARK DRIVE                                                       
send to:                        WAYNE, PA 19087-1815                        All written requests should be
                                                                            mailed to one of the addresses
                                                                            indicated for new accounts. Do
                                                                            not send registered or express
                                                                            mail to the post office box
                                                                            address.

                                                     VANGUARD BOND INDEX FUND
                                                  Total Bond Market Portfolio -- 84
                                                  Short-Term Bond Portfolio -- 132
                                                  Intermediate-Term Bond Portfolio -- 314
                                                  Long-Term Bond Portfolio -- 522
                                ------------------------------------------------------------
PURCHASING BY WIRE                                CORESTATES BANK, N.A.
                                                  ABA 031000011
Money should be                                   CORESTATES NO. 0101 9897
wired to:                                         ATTN: VANGUARD
                                                  VANGUARD BOND INDEX FUND
BEFORE WIRING                                     NAME OF PORTFOLIO
                                                  ACCOUNT NUMBER
Please contact                                    ACCOUNT REGISTRATION
Client Services
(1-800-662-2739)
</TABLE>

                      To assure proper receipt, please be sure your bank
                      includes the name of the Portfolio, the account number
                      Vanguard has assigned to you and the eight-digit
                      CoreStates number. If you are opening a new account,
                      please complete the Account Registration Form and mail it
                      to the "New Account" address above after completing your
                      wire arrangement. NOTE: Federal Funds wire purchase orders
                      will be accepted only when the Fund and Custodian Bank are
                      open for business.
- --------------------------------------------------------------------------------
PURCHASING BY
EXCHANGE (from a
Vanguard account)     You may open an account or purchase additional shares by
                      making an exchange from an existing Vanguard Fund account.
                      However, the Fund reserves the right to refuse any
                      exchange purchase request. Call our Client Services
                      Department

                                       25
<PAGE>   28
 
                      (1-800-662-2739) for assistance. The new account will have
                      the same registration as the existing account.
- --------------------------------------------------------------------------------
 
PURCHASING BY
FUND EXPRESS
Special Purchase and
Automatic Investment  The Fund Express Special Purchase option lets you move
                      money from your bank account to your Vanguard account on
                      an "as needed" basis. Or if you choose the Automatic
                      Investment option, money will be moved automatically from
                      your bank account to your Vanguard account on the schedule
                      (monthly, bimonthly [every other month], quarterly,
                      semiannually, or annually) you select. To establish these
                      Fund Express options, please provide the appropriate
                      information on the Account Registration Form. We will send
                      you a confirmation of your Fund Express enrollment; please
                      wait two weeks before using the service.
- --------------------------------------------------------------------------------
 
CHOOSING A
DISTRIBUTION
OPTION                You must select one of four distribution options:
 
                      1. AUTOMATIC REINVESTMENT OPTION -- Both dividend and
                         capital gains distributions will be reinvested in
                         additional Fund shares. This option will be selected
                         for you automatically unless you specify one of the
                         other options.
 
                      2. CASH DIVIDEND OPTION -- Your dividends will be paid in
                         cash and your capital gains will be reinvested in
                         additional Fund shares.
 
   
                      3. CASH CAPITAL GAINS OPTION -- Your capital gains
                         distributions will be paid in cash and your dividends
                         will be reinvested in additional Fund Shares.
    
 
                      4. ALL CASH OPTION -- Both dividend and capital gains
                         distributions will be paid in cash.
 
                      You may change your option by calling our Client Services
                      Department (1-800-662-2739).
 
                      If a shareholder has chosen to receive dividend and/or
                      capital gains distributions in cash, and the postal or
                      other delivery service is unable to deliver checks to the
                      shareholder's address of record, we will change the
                      distribution option so that all dividends and other
                      distributions are automatically reinvested in additional
                      shares. We will not pay interest on uncashed distribution
                      checks.
 
                      In addition, an option to invest your cash dividend and/or
                      capital gains distributions in another Vanguard Fund
                      account is available. Please call our Client Services
                      Department (1-800-662-2739) for information. You may also
                      elect Vanguard Dividend Express which allows you to
                      transfer your cash dividend and/or capital gains
                      distributions automatically to your bank account. Please
                      see "Other Vanguard Services" for more information.
- --------------------------------------------------------------------------------
 
TAX CAUTION
INVESTORS SHOULD ASK
ABOUT THE TIMING OF
CAPITAL GAINS AND
DIVIDEND DISTRIBUTIONS
BEFORE INVESTING      Under Federal tax laws, the Fund is required to distribute
                      net capital gains and dividend income to Fund
                      shareholders. These distributions are made to all
                      shareholders who own Fund shares as of the distribution's
                      record date, regardless of how long the shares have been
                      owned. Purchasing shares just prior to the record date
                      could have a significant impact on your tax liability for
                      the year. For example, if you purchase shares immediately
                      prior to the record date of a sizable capital gains
                      distribution, you will be assessed taxes on the amount of
                      the capital gains
 
                                       26
<PAGE>   29
 
                      distribution later paid even though you owned the Fund
                      shares for just a short period of time. (Taxes are due on
                      the distributions even if the dividend or capital gain is
                      reinvested in additional Fund shares.) While the total
                      value of your investment will be the same after the
                      capital gains distribution -- the amount of the capital
                      gains distribution will offset the drop in the net asset
                      value of the shares -- you should be aware of the tax
                      implications the timing of your purchase may have.
 
                      Prospective investors should, therefore, inquire about
                      potential distributions before investing. The Fund's
                      annual capital gains distributions normally occur in
                      December, while income dividends are generally paid on the
                      first day of each month. In addition, the Fund may
                      occasionally be required to make supplemental dividend or
                      capital gains distributions at some other time during the
                      year. For additional information on distributions and
                      taxes, see the section titled "Dividends, Capital Gains,
                      and Taxes."
- --------------------------------------------------------------------------------
 
IMPORTANT
INFORMATION

ESTABLISHING OPTIONAL
SERVICES              The easiest way to establish optional Vanguard services on
                      your account is to select the options you desire when you
                      complete your Account Registration Form.
 
                      IF YOU WISH TO ADD OPTIONS LATER, YOU MAY NEED TO PROVIDE
                      VANGUARD WITH ADDITIONAL INFORMATION AND A SIGNATURE
                      GUARANTEE. PLEASE CALL OUR CLIENT SERVICES DEPARTMENT
                      (1-800-662-2739) FOR FURTHER ASSISTANCE.
 
SIGNATURE
GUARANTEES            For our mutual protection, we may require a signature
                      guarantee on certain written transaction requests. A
                      signature guarantee verifies the authenticity of your
                      signature and may be obtained from banks, brokers and any
                      other guarantor that Vanguard deems acceptable. A
                      SIGNATURE GUARANTEE CANNOT BE PROVIDED BY A NOTARY PUBLIC.
 
CERTIFICATES          Share certificates will be issued upon request. If a
                      certificate is lost, you may incur an expense to replace
                      it.
 
BROKER/DEALER
PURCHASES             If you purchase shares in Vanguard Funds through a
                      registered broker/dealer or investment adviser, the
                      broker/dealer or adviser may charge a service fee.
 
CANCELLING TRADES     The Fund will not cancel any trade (e.g., a purchase,
                      exchange or redemption) believed to be authentic, once the
                      trade request has been received in writing or by
                      telephone.
 
ELECTRONIC
PROSPECTUS
DELIVERY              You may receive a prospectus for the Fund or any of the
                      Vanguard Funds in an electronic format through Vanguard's
                      website at www.vanguard.com. For additional information
                      please see "Other Vanguard Services -- Computer Access."
- --------------------------------------------------------------------------------
 
WHEN YOUR
ACCOUNT WILL
BE CREDITED           The trade date is the date on which your account is
                      credited. If your purchase is made by check, Federal Funds
                      wire, or exchange, and is received by the close of trading
                      on the New York Stock Exchange (the "Exchange"), generally
                      4:00 p.m. Eastern time, your trade date is the day of
                      receipt. If your purchase is received after the close of
                      the Exchange, your trade date is the next business day.
                      Your shares are purchased at the net asset value
                      determined on your trade date. You will begin to earn
                      dividends on the calendar day following the trade date.
                      (For a Friday trade date, you will begin earning dividends
                      on Saturday).
 
                                       27
<PAGE>   30
 
                      In order to prevent lengthy processing delays caused by
                      the clearing of foreign checks, Vanguard will only accept
                      a foreign check which has been drawn in U.S. dollars and
                      has been issued by a foreign bank with a U.S.
                      correspondent bank. The name of the U.S. correspondent
                      bank must be printed on the face of the foreign check.
- --------------------------------------------------------------------------------
 
SELLING YOUR
SHARES                You may withdraw any portion of the funds in your account
                      by redeeming shares at any time. (Please see "Important
                      Redemption Information.") You generally may initiate a
                      request by writing or by telephoning. Your redemption
                      proceeds are normally mailed, credited or
                      wired -- depending upon the method of withdrawal you have
                      PREVIOUSLY chosen -- within two business days after the
                      receipt of the request in Good Order. No interest will
                      accrue on amounts represented by uncashed redemption
                      checks.
- --------------------------------------------------------------------------------
SELLING BY WRITING
A CHECK               You may withdraw funds from your account by writing a
                      check payable in the amount of $250 or more. When a check
                      is presented for payment to the Fund's agent, CoreStates
                      Bank, the Fund will redeem sufficient shares in your
                      account at the next-determined net asset value to cover
                      the amount of the check. You cannot write a Vanguard check
                      to redeem shares that you purchased by check within the
                      previous ten days.
 
                      In order to establish the checkwriting option on your
                      account, all registered shareholders must sign a signature
                      card. After your completed signature card is received by
                      the Fund, an initial supply of checks will be mailed
                      within 10 business days. There is no charge for checks or
                      for their clearance. CORPORATIONS, TRUSTS, POWERS OF
                      ATTORNEY AND OTHER ORGANIZATIONS SHOULD CALL OR WRITE OUR
                      CLIENT SERVICES DEPARTMENT (1-800-662-2739) BEFORE
                      SUBMITTING SIGNATURE CARDS, AS ADDITIONAL DOCUMENTS MAY BE
                      REQUIRED TO ESTABLISH THE CHECKWRITING SERVICE.
 
                      Before establishing the checkwriting option, you should be
                      aware that:
 
                      1. Writing a check (a redemption of shares) is a taxable
                         event.
                      2. The Fund does not allow an account to be closed through
                         the checkwriting option.
                      3. Vanguard cannot guarantee a stop payment on any check.
                         If you wish to reverse a stop payment order, you must
                         do so in writing.
                      4. Shares held in certificate form cannot be redeemed
                         using the checkwriting option.
                      5. The Fund reserves the right to terminate or alter this
                         service at any time.
- --------------------------------------------------------------------------------
SELLING BY MAIL       Requests should be mailed to THE VANGUARD GROUP, VANGUARD
                      BOND INDEX FUND, P.O. BOX 1120, VALLEY FORGE, PA
                      19482-1120. (For express or registered mail, send your
                      request to The Vanguard Group, Vanguard Bond Index Fund,
                      455 Devon Park Drive, Wayne, PA 19087-1815.)
 
                      The redemption price of shares will be the Portfolio's net
                      asset value next determined after Vanguard has received
                      all required documents in Good Order.
- --------------------------------------------------------------------------------
DEFINITION OF
GOOD ORDER            GOOD ORDER means that the request includes the following:
 
                      1. The account number and Portfolio name.
 
                                       28
<PAGE>   31
 
                      2. The amount of the transaction (specified in dollars or
                         shares).
                      3. The signatures of all owners EXACTLY as they are
                         registered on the account.
                      4. Any required signature guarantees.
                      5. Other supporting legal documentation that may be
                         required in the case of estates, corporations, trusts,
                         and certain other accounts.
                      6. Any certificates you are holding for the account.
 
                      IF YOU HAVE QUESTIONS ABOUT THIS DEFINITION AS IT PERTAINS
                      TO YOUR REQUEST, PLEASE CALL CLIENT SERVICES
                      (1-800-662-2739).
- --------------------------------------------------------------------------------
SELLING BY TELEPHONE  To sell shares by telephone, you or your pre-authorized
                      representative may call our Client Services Department at
                      1-800-662-2739. For telephone redemptions, you may have
                      the proceeds sent to you either by mail or by wire. In
                      addition to the details below, please see "Important
                      Information About Telephone Transactions."
 
                      BY MAIL: Telephone mail redemption is automatically
                      established on your account unless you indicate otherwise
                      on your Account Registration Form. You may redeem any
                      amount by calling Vanguard. The proceeds will be paid to
                      the registered shareholders and mailed to the address of
                      record. PLEASE NOTE: As a protection against fraud, your
                      telephone mail redemption privilege will be suspended for
                      15 calendar days following any expedited address change to
                      your account. An expedited address change is one that is
                      made by telephone, or in writing, without the signatures
                      of all account owners.
 
                      BY WIRE: Telephone wire redemption must be specifically
                      elected for your account. The best time to elect telephone
                      wire redemption is at the time you complete your Account
                      Registration Form. If you do not presently have telephone
                      wire redemption and wish to establish it, please contact
                      Client Services.
 
                      With the wire redemption option, you may withdraw a
                      minimum of $1,000 and have the amount wired directly to
                      your bank account. Wire redemptions less than $5,000 are
                      subject to a $5 charge deducted by Vanguard. There is no
                      Vanguard charge for wire redemptions of $5,000 or more.
                      However, your bank may assess a separate fee to accept
                      incoming wires.
 
                      A request to change the bank associated with your wire
                      redemption option must be received in writing, signed by
                      each registered shareholder, and accompanied by a voided
                      check or preprinted deposit slip. A signature guarantee is
                      required if your bank registration is not identical to
                      your Vanguard Fund account registration.
- --------------------------------------------------------------------------------
SELLING BY FUND
EXPRESS

Automatic Withdrawal
& Special Redemption  If you select the Fund Express Automatic Withdrawal
                      option, money will be automatically moved from your
                      Vanguard Fund account to your bank account according to
                      the schedule you have selected. The Special Redemption
                      option lets you move money from your Vanguard account to
                      your bank account on an "as needed" basis. To establish
                      these Fund Express options, please provide the appropriate
                      information on the Account Registration Form. We will send
                      you a confirmation of your Fund Express service; please
                      wait two weeks before using the service.
- --------------------------------------------------------------------------------
 
                                       29
<PAGE>   32
 
SELLING BY EXCHANGE   You may sell shares of a Portfolio by making an exchange
                      into another Vanguard Fund account. Please see "Exchanging
                      Your Shares" for details.
- --------------------------------------------------------------------------------
IMPORTANT REDEMPTION
INFORMATION           Shares purchased by check or Fund Express may be redeemed
                      at any time. However, your redemption proceeds will not be
                      paid until payment for the purchase is collected, which
                      may take up to ten calendar days.
- --------------------------------------------------------------------------------
DELIVERY OF
REDEMPTION
PROCEEDS              Redemption requests received by telephone prior to the
                      close of the Exchange are processed on the day of receipt
                      and the redemption proceeds are normally sent on the
                      following business day.
 
                      Redemption requests received by telephone after the close
                      of the Exchange are processed on the business day
                      following receipt and the proceeds are normally sent on
                      the second business day following receipt.
 
                      Redemption proceeds must be sent to you within seven days
                      of receipt of your request in Good Order except as
                      described above in "Important Redemption Information."
 
                      If you experience difficulty in making a telephone
                      redemption during periods of drastic economic or market
                      changes, your redemption request may be made by regular or
                      express mail. It will be implemented at the net asset
                      value next determined after your request has been received
                      by Vanguard in Good Order. The Fund reserves the right to
                      revise or terminate the telephone redemption privilege at
                      any time.
 
                      The Fund may suspend the redemption right or postpone
                      payment at times when the New York Stock Exchange is
                      closed or under any emergency circumstances as determined
                      by the United States Securities and Exchange Commission.
 
                      If the Board of Directors determines that it would be
                      detrimental to the best interests of the Fund's remaining
                      shareholders to make payment in cash, the Fund may pay
                      redemption proceeds in whole or in part by a distribution
                      in kind of readily marketable securities.
- --------------------------------------------------------------------------------
VANGUARD'S AVERAGE
COST STATEMENT        If you make a redemption from a qualifying account,
                      Vanguard will send you an Average Cost Statement which
                      provides you with the tax basis of the shares you
                      redeemed. Please see "Statements and Reports" for
                      additional information.
- --------------------------------------------------------------------------------
LOW BALANCE FEE
AND MINIMUM
ACCOUNT BALANCE
REQUIREMENT           Due to the relatively high cost of maintaining smaller
                      accounts, the Fund will automatically deduct a $10 annual
                      fee in either June or December from non-retirement
                      accounts with balances falling below $2,500 ($500 for
                      Uniform Gifts/Transfers to Minors Act accounts). The fee
                      generally will be waived for investors whose aggregate
                      Vanguard assets exceed $50,000.
 
                      In addition, the Fund reserves the right to liquidate any
                      non-retirement account that is below the minimum initial
                      investment amount of $3,000. If at any time the total
                      investment does not have a value of at least $3,000, you
                      may be notified that your account is below the Fund's
                      minimum account balance requirement. You would
 
                                       30
<PAGE>   33
 
                      then be allowed 60 days to make an additional investment
                      before the account is liquidated. Proceeds would be
                      promptly paid to the registered shareholder.
 
                      Vanguard will not liquidate your account if it has fallen
                      below $3,000 solely as a result of declining markets
                      (i.e., a decline in a Portfolio's net asset value).
- --------------------------------------------------------------------------------
 
EXCHANGING YOUR
SHARES                Should your investment goals change, you may exchange your
                      shares of Vanguard Bond Index Fund for those of other
                      available Vanguard Funds.
 
   
EXCHANGING BY
TELEPHONE
Call Client Services
(1-800-662-2739)      When exchanging shares by telephone, please have ready the
                      Fund name, account number, Social Security number or
                      employer identification number listed on the account, and
                      the exact name and address in which the account is
                      registered. Only the registered shareholder may complete
                      such an exchange. Requests for telephone exchanges
                      received prior to the close of trading on the Exchange are
                      processed at the close of business that same day. Requests
                      received after the close of the Exchange are processed the
                      next business day. TELEPHONE EXCHANGES ARE NOT ACCEPTED
                      INTO OR FROM NON-RETIREMENT INVESTMENTS IN VANGUARD INDEX
                      TRUST, VANGUARD BALANCED INDEX FUND, VANGUARD
                      INTERNATIONAL EQUITY INDEX FUND, VANGUARD REIT INDEX
                      PORTFOLIO, VANGUARD TOTAL INTERNATIONAL PORTFOLIO, and
                      VANGUARD GROWTH AND INCOME PORTFOLIO. If you experience
                      difficulty in making a telephone exchange, your exchange
                      request may be made by regular or express mail, and it
                      will be implemented at the closing net asset value on the
                      date received by Vanguard provided the request is received
                      in Good Order.
    
- --------------------------------------------------------------------------------
EXCHANGING BY MAIL    Please be sure to include on your exchange request the
                      name and account number of your current Portfolio, the
                      name of the Fund you wish to exchange into, the amount you
                      wish to exchange, and the signatures of all registered
                      account holders. Send your request to THE VANGUARD GROUP,
                      VANGUARD BOND INDEX FUND, P.O. BOX 1120, VALLEY FORGE, PA
                      19482-1120. (For express or registered mail, send your
                      request to The Vanguard Group, Vanguard Bond Index Fund,
                      455 Devon Park Drive, Wayne, PA 19087-1815.)
- --------------------------------------------------------------------------------
EXCHANGING ONLINE     You may use your personal computer to exchange shares of
                      most Vanguard funds by accessing our website
                      (www.vanguard.com). To establish this service for your
                      account, you must first register through the website. We
                      will then send to you, by mail, an account access password
                      that will enable you to make online exchanges.
 
                      The Vanguard funds that you cannot purchase or sell
                      through online exchange are VANGUARD INDEX TRUST, VANGUARD
                      BALANCED INDEX FUND, VANGUARD INTERNATIONAL EQUITY INDEX
                      FUND, VANGUARD REIT INDEX PORTFOLIO, VANGUARD TOTAL
                      INTERNATIONAL PORTFOLIO, AND VANGUARD GROWTH AND INCOME
                      PORTFOLIO (formerly known as Vanguard Quantitative
                      Portfolios). These funds do permit online exchanges within
                      IRAs and other retirement accounts.
- --------------------------------------------------------------------------------
IMPORTANT EXCHANGE
INFORMATION           Before you make an exchange, you should consider the
                      following:
 
                      - Please read the Fund's prospectus before making an
                        exchange. For a copy and for answers to any questions
                        you may have, call our Investor Information Department
                        (1-800-662-7447).
 
                                       31
<PAGE>   34
 
                      - An exchange is treated as a redemption and a purchase.
                        Therefore, you could realize a taxable gain or loss on
                        the transaction.
 
                      - Exchanges by telephone are accepted only if the
                        registrations and the taxpayer identification numbers of
                        the two accounts are identical.
 
                      - To exchange into an account with a different
                        registration (including a different name, address, or
                        taxpayer identification number), you must provide
                        Vanguard with written instructions that include the
                        guaranteed signatures of all current account owners.
 
                      - New accounts are not currently accepted in
                        Vanguard/Windsor Fund.
 
                      - The redemption price of shares redeemed by exchange is
                        the net asset value next determined after Vanguard has
                        received all required documentation in Good Order.
 
                      - When opening a new account by exchange, you must meet
                        the minimum investment requirement of the new Fund.
 
                      Every effort will be made to maintain the exchange
                      privilege. However, the Fund reserves the right to revise
                      or terminate its provisions, limit the amount of, or
                      reject any exchange, as deemed necessary, at any time.
- --------------------------------------------------------------------------------
 
EXCHANGE
PRIVILEGE
LIMITATIONS           The Fund's exchange privilege is not intended to afford
                      shareholders a way to speculate on short-term movements in
                      the market. Accordingly, in order to prevent excessive use
                      of the exchange privilege that may potentially disrupt the
                      management of the Fund and increase transaction costs, the
                      Fund has established a policy of limiting excessive
                      exchange activity.
 
                      Exchange activity generally will not be deemed excessive
                      if limited to TWO SUBSTANTIVE EXCHANGE REDEMPTIONS (AT
                      LEAST 30 DAYS APART) from a Portfolio of the Fund during
                      any twelve-month period. "Substantive" means either a
                      dollar amount or a series of movements between Vanguard
                      Funds that Vanguard determines, in its sole discretion,
                      could have an adverse impact on the management of the
                      Fund. Notwithstanding these limitations, the Fund reserves
                      the right to reject any purchase request (including
                      exchange purchases from other Vanguard portfolios) that is
                      reasonably deemed to be disruptive to efficient portfolio
                      management.
- --------------------------------------------------------------------------------
 
IMPORTANT
INFORMATION
ABOUT TELEPHONE
TRANSACTIONS          The ability to initiate redemptions (except wire or Fund
                      Express redemptions) and exchanges by telephone is
                      automatically established on your account unless you
                      request in writing that telephone transactions on your
                      account not be permitted. The ability to initiate wire
                      redemptions by telephone will be established on your
                      account only if you specifically elect this option in
                      writing.
 
                      To protect your account from losses resulting from
                      unauthorized or fraudulent telephone instructions,
                      Vanguard adheres to the following security procedures:
 
                      1. SECURITY CHECK.  To request a transaction by telephone,
                         the caller must know (i) the name of the Portfolio;
                         (ii) the 10-digit account number; (iii) the exact name
 
                                       32
<PAGE>   35
 
                        and address used in the registration; and (iv) the
                        Social Security or employer identification number listed
                        on the account.
 
                      2. PAYMENT POLICY.  The proceeds of any telephone
                         redemption by mail will be made payable to the
                         registered shareowner and mailed to the address of
                         record only. In the case of a telephone redemption by
                         wire, the wire transfer will be made only in accordance
                         with the shareowner's prior written instructions.
 
                      Neither the Fund nor Vanguard will be responsible for the
                      authenticity of transaction instructions received by
                      telephone, provided that reasonable security procedures
                      have been followed. Vanguard believes that the security
                      procedures described above are reasonable, and that if
                      such procedures are followed, you will bear the risk of
                      any losses resulting from unauthorized or fraudulent
                      telephone transactions on your account.
- --------------------------------------------------------------------------------
 
TRANSFERRING
REGISTRATION          You may transfer the registration of any of your Fund
                      shares to another person by completing a transfer form and
                      sending it to: THE VANGUARD GROUP, ATTENTION: TRANSFER
                      DEPARTMENT, P.O. BOX 1110, VALLEY FORGE, PA 19482-1110.
                      The request must be in Good Order. To obtain a transfer
                      form, please call our Client Services Department
                      (1-800-662-2739).
- --------------------------------------------------------------------------------
 
STATEMENTS AND
REPORTS               Vanguard will send you a confirmation statement each time
                      you initiate a transaction in your account. You will also
                      receive a comprehensive account statement at the end of
                      each calendar quarter. The fourth-quarter statement will
                      be a year-end statement, listing all transaction activity
                      for the entire calendar year.
 
                      Vanguard's Average Cost Statement provides you with the
                      average cost of shares redeemed from your account during
                      the calendar year, using the average cost single category
                      method. This service is available for most taxable
                      accounts opened since January 1, 1986. In general,
                      investors who redeemed shares from a qualifying Vanguard
                      account may expect to receive their Average Cost Statement
                      with their Portfolio Summary Statement. Please call our
                      Client Services Department (1-800-662-2739) for
                      information.
 
                      A checkwriting statement will be sent monthly to
                      shareholders using Vanguard's checkwriting option. Our
                      clear, easy-to-use statement provides images of the front
                      and back of each checkwriting draft paid in the previous
                      month. This consolidated statement is sent instead of the
                      original canceled drafts, which will not be returned.
 
                      Financial reports on the Fund will be mailed to you
                      semiannually, according to the Fund's fiscal year-end. To
                      keep the Fund's costs as low as possible (so that you and
                      other shareholders can keep more of the Fund's investment
                      earnings), Vanguard attempts to eliminate duplicate
                      mailings to the same address. When we find that two or
                      more Fund shareholders have the same last name and
                      address, we send just one Fund report to that
                      address -- instead of mailing separate reports to each
                      shareholder. If you want us to send separate reports,
                      however, you may notify our Investor Information
                      Department at 1-800-662-7447.
- --------------------------------------------------------------------------------
 
                                       33
<PAGE>   36
 
OTHER VANGUARD
SERVICES              For more information about any of these services, please
                      call our Investor Information Department at
                      1-800-662-7447.
 
VANGUARD DIRECT
DEPOSIT SERVICE       With Vanguard's Direct Deposit Service, most U.S.
                      Government checks (including Social Security and military
                      pension checks) and private payroll checks may be
                      automatically deposited into your Vanguard Fund account.
                      Separate brochures and forms are available for direct
                      deposit of U.S. Government and private payroll checks.
 
VANGUARD AUTOMATIC
EXCHANGE SERVICE      Vanguard's Automatic Exchange Service allows you to move
                      money automatically among your Vanguard Fund accounts. For
                      instance, the service can be used to "dollar cost average"
                      from a money market portfolio into a stock or bond fund or
                      to contribute to an IRA or other retirement plan. Please
                      contact our Client Services Department at 1-800-662-2739
                      for additional information.
 
VANGUARD FUND
EXPRESS               Vanguard's Fund Express allows you to transfer money
                      between your Fund account and your account at a bank,
                      savings and loan association, or a credit union that is a
                      member of the Automated Clearing House (ACH) system. You
                      may elect this service on the Account Registration Form or
                      call our Investor Information Department (1-800-662-7447)
                      for a Fund Express application.
 
                      Special rules govern how your Fund Express purchases or
                      redemptions are credited to your account. In addition,
                      some services of Fund Express cannot be used with specific
                      Vanguard Funds. For more information, please refer to the
                      Vanguard Fund Express brochure.
 
VANGUARD DIVIDEND
EXPRESS               Vanguard's Dividend Express allows you to transfer your
                      dividend and/or capital gains distributions automatically
                      from your Fund account, one business day after the Fund's
                      payable date, to your account at a bank, savings and loan
                      association, or a credit union that is a member of the
                      Automated Clearing House (ACH) system. You may elect this
                      service on the Account Registration Form or call our
                      Investor Information Department (1-800-662-7447) for a
                      Vanguard Dividend Express application.
 
VANGUARD
TELE-ACCOUNT(R)       Vanguard Tele-Account is a convenient, automated service
                      that provides share price, price change and yield
                      quotations on Vanguard Funds through any TouchTone(TM)
                      telephone. This service also lets you obtain information
                      about your account balance, your last transaction, and
                      your most recent dividend or capital gains payment. In
                      addition, you may perform investment exchanges of Vanguard
                      Fund shares and redemptions by check using Tele-Account.
                      To contact Vanguard's Tele-Account service, dial
                      1-800-ON-BOARD (1-800-662-6273). A brochure offering
                      detailed operating instructions is available from our
                      Investor Information Department (1-800-662-7447).
 
COMPUTER ACCESS
 
VANGUARD ONLINE
www.vanguard.com      Use your personal computer to learn more about Vanguard's
                      funds and services; keep in touch with your Vanguard
                      accounts; map out a long-term investment strategy;
                      initiate certain transactions; and ask questions, make
                      suggestions, and send messages to Vanguard.
 
                                       34
<PAGE>   37
 
                      Our education-oriented website provides timely news and
                      information about Vanguard's funds and services; an online
                      "university" that offers a variety of mutual fund classes;
                      and easy-to-use, interactive tools to help you create your
                      own investment and retirement strategies.
- --------------------------------------------------------------------------------
 
                                       35
<PAGE>   38
 
                      [THIS PAGE INTENTIONALLY LEFT BLANK]
<PAGE>   39
 
- --------------------------------------------------------------------------------
 
<TABLE>
<S>                             <C>                                   <C>
      P084                                                                                                                    LOGO
                                LOGO                                                                                          LOGO
                                ---------------------------                                  P   R   O   S   P   E   C   T   U   S
                                THE VANGUARD GROUP                                                                  APRIL 17, 1998
                                P.O. Box 2600
                                Valley Forge, PA 19482                                                                        LOGO
                                INVESTOR INFORMATION
                                DEPARTMENT:
                                1-800-662-7447 (SHIP)
                                CLIENT SERVICES
                                DEPARTMENT:
                                1-800-662-2739 (CREW)
                                TELE-ACCOUNT FOR
                                24-HOUR ACCESS:
                                1-800-662-6273 (ON-BOARD)
                                TELECOMMUNICATION SERVICE
                                FOR THE HEARING-IMPAIRED:
                                1-800-662-2738
                                TRANSFER AGENT:
                                The Vanguard Group, Inc.
                                P.O. Box 2600
                                Valley Forge, PA 19482
</TABLE>
 
- --------------------------------------------------------------------------------
<PAGE>   40
 
- --------------------------------------------------------------------------------
 
================================================================================
 
VANGUARD BOND INDEX FUND                          A Member of The Vanguard Group
 
- --------------------------------------------------------------------------------
 
- --------------------------------------------------------------------------------
 
PROSPECTUS -- APRIL 17, 1998
- --------------------------------------------------------------------------------
 
FUND INFORMATION: PARTICIPANT SERVICES -- 1-800-523-1188
- --------------------------------------------------------------------------------
 
INVESTMENT
OBJECTIVE
AND POLICIES        Vanguard Bond Index Fund, Inc. (the "Fund"), is an open-end,
                    diversified investment company designed as an "index fund."
                    The Fund consists of four distinct portfolios, each of which
                    invests in fixed-income securities with prescribed maturity
                    and credit quality standards. The objective of each
                    Portfolio is to duplicate the total return (income plus
                    capital change) of publicly-traded investment grade
                    fixed-income securities in the aggregate by attempting to
                    duplicate the investment performance of certain investment
                    grade bond indexes. The Fund invests in a diversified
                    portfolio of U.S. Government and corporate bonds and
                    mortgage-backed securities. There is no assurance that a
                    Portfolio will achieve its stated objective. Shares of the
                    Fund are neither insured nor guaranteed by any agency of the
                    U.S. Government, including the FDIC.
- --------------------------------------------------------------------------------
 
IMPORTANT NOTE      This Prospectus is intended exclusively for participants in
                    employer-sponsored retirement or savings plans, such as
                    tax-qualified pension and profit-sharing plans and 401(k)
                    thrift plans, as well as 403(b) custodial accounts for
                    non-profit educational and charitable organizations. Another
                    version of this Prospectus, containing information on how to
                    open a personal investment account with the Fund, is
                    available for individual investors. To obtain a copy of that
                    version of the Prospectus, please call 1-800-662-7447. For
                    investors investing $10 million or more in the Total Bond
                    Market Portfolio and who meet certain administrative
                    criteria, the Fund offers a second class of shares, Total
                    Bond Market Portfolio Institutional Shares, which is offered
                    through a separate prospectus. To obtain information on the
                    Total Bond Market Portfolio Institutional Shares, please
                    call 1-800-523-8066.
- --------------------------------------------------------------------------------
 
OPENING AN
ACCOUNT             The Fund is an investment option under a retirement or
                    savings program sponsored by your employer. The
                    administrator of your retirement plan or your employee
                    benefits office can provide you with detailed information on
                    how to participate in your plan and how to elect the Fund as
                    an investment option.
 
                    If you have any questions about the Fund, please contact
                    Participant Services at 1-800-523-1188. If you have any
                    questions about your plan account, contact your plan
                    administrator or the organization that provides
                    recordkeeping services for your plan.
- --------------------------------------------------------------------------------
 
ABOUT THIS
PROSPECTUS          This Prospectus is designed to set forth concisely the
                    information you should know about the Fund before you
                    invest. It should be retained for future reference. A
                    "Statement of Additional Information" containing additional
                    information about the Fund has been filed with the
                    Securities and Exchange Commission. This Statement is dated
                    April 17, 1998 and has been incorporated by reference into
                    this Prospectus. A copy may be obtained without charge by
                    writing to the Fund, calling Participant Services at
                    1-800-523-1188 or visiting the Securities and Exchange
                    Commission's website (www.sec.gov).
- --------------------------------------------------------------------------------
 
TABLE OF CONTENTS
 
<TABLE>
<CAPTION>
                Page                                         Page                                         Page
<S>                                          <C>                                          <C>
Highlights ..........................  2     Investment Risks .....................10     Dividends, Capital Gains and Taxes .. 19
Fund Expenses .......................  4     Who Should Invest ................... 13     The Share Price of Each Portfolio ... 20
Financial Highlights ................  5     Implementation of Policies .......... 13     General Information ................. 20
Yield and Total Return ..............  7     Investment Limitations .............. 16
                                             Management of the Fund .............. 17     SERVICE GUIDE
FUND INFORMATION                             Investment Adviser .................. 17     Participating in Your Plan .......... 22
Investment Objective ................. 8     Performance Record .................. 18
Investment Policies .................. 8
</TABLE>

- --------------------------------------------------------------------------------

THESE SECURITIES HAVE NOT BEEN APPROVED OR DISAPPROVED BY THE SECURITIES AND
EXCHANGE COMMISSION NOR HAS THE SECURITIES AND EXCHANGE COMMISSION PASSED UPON
THE ACCURACY OR ADEQUACY OF THIS PROSPECTUS. ANY REPRESENTATION TO THE CONTRARY
IS A CRIMINAL OFFENSE.
- --------------------------------------------------------------------------------

- --------------------------------------------------------------------------------
<PAGE>   41
 
                                   HIGHLIGHTS
 
OBJECTIVE AND
POLICIES              The Fund is a no-load, open-end diversified investment
                      company designed as an "index" fund. The Fund consists of
                      four distinct Portfolios, each of which invests in
                      fixed-income securities with prescribed maturity and
                      credit quality standards in order to match the investment
                      performance of certain investment grade bond indexes.
                      There is no assurance that any of the Fund's Portfolios
                      will achieve its stated objective.                  PAGE 8
- --------------------------------------------------------------------------------
 
FOUR SEPARATE
PORTFOLIOS            Investors may choose to invest in any of four Portfolios
                      of the Fund:
 
                      TOTAL BOND MARKET PORTFOLIO -- seeks to match the
                      investment performance of the Lehman Brothers Aggregate
                      Bond Index, a broad market-weighted index which
                      encompasses U.S. Treasury and agency securities,
                      investment grade corporate bonds, international
                      (dollar-denominated) investment grade bonds, and mortgage-
                      backed securities.
 
                      SHORT-TERM BOND PORTFOLIO -- seeks to match the investment
                      performance of the Lehman Brothers Mutual Fund Short (1-5)
                      Government/Corporate Index, a market-weighted index which
                      encompasses U.S. Treasury and agency securities and
                      investment grade corporate and international
                      (dollar-denominated) bonds, with maturities between 1 and
                      5 years.
 
                      INTERMEDIATE-TERM BOND PORTFOLIO -- seeks to match the
                      investment performance of the Lehman Brothers Mutual Fund
                      Intermediate (5-10) Government/Corporate Index, a
                      market-weighted index which encompasses U.S. Treasury and
                      agency securities and investment grade corporate and
                      international (dollar-denominated) bonds, with maturities
                      between 5 and 10 years.
 
                      LONG-TERM BOND PORTFOLIO -- seeks to match the investment
                      performance of the Lehman Brothers Long (10+)
                      Government/Corporate Index, a market-weighted index which
                      encompasses U.S. Treasury and agency securities and
                      investment grade corporate and international
                      (dollar-denominated) bonds, with maturities greater than
                      10 years.                                           PAGE 8
- --------------------------------------------------------------------------------
 
RISK
CHARACTERISTICS       Investors in the Fund are exposed to four types of risk
                      from fixed-income securities. (1) INTEREST RATE RISK is
                      the potential for fluctuations in bond prices due to
                      changing interest rates. (2) INCOME RISK is the potential
                      for a decline in a Portfolio's income due to falling
                      market interest rates. (3) CREDIT RISK is the possibility
                      that a bond issuer will fail to make timely payments of
                      either interest or principal to a Portfolio. (4)
                      PREPAYMENT RISK (applicable to the Total Bond Market
                      Portfolio which invests in mortgage-backed securities) or
                      CALL RISK (for corporate bonds) is the likelihood that,
                      during periods of falling interest rates, callable
                      securities with high stated interest rates will be prepaid
                      (or "called") prior to maturity, requiring a Portfolio to
                      invest the proceeds at generally lower interest rates.
 
                                        2
<PAGE>   42
 
                      The following chart summarizes interest rate, income,
                      credit and prepayment/call risks for the four Portfolios
                      of the Fund. As shown, interest rate risk should be low
                      for the Short-Term Bond Portfolio, moderate for the Total
                      Bond Market and Intermediate-Term Bond Portfolios, and
                      high for the Long-Term Bond Portfolio.             PAGE 10
- --------------------------------------------------------------------------------
 
                                             RISK SUMMARY
 
<TABLE>
<CAPTION>
                               -------------------------------------------------------------------------------
                                                                 INTEREST    INCOME   CREDIT   PREPAYMENT/
                                            PORTFOLIO            RATE RISK    RISK     RISK     CALL RISK
                               <S> <C>                           <C>         <C>      <C>      <C>         <C>
                               -------------------------------------------------------------------------------
                                   Total Bond Market              Medium     Medium    Low       Medium
                                   Short-Term Bond                Low        High      Low       Low
                                   Intermediate-Term Bond         Medium     Medium    Low       Low
                                   Long-Term Bond                 High       Low       Low       Medium
                               -------------------------------------------------------------------------------
</TABLE>
 
- --------------------------------------------------------------------------------
 
   
THE VANGUARD
GROUP                 The Fund is a member of The Vanguard Group of Investment
                      Companies, a group of more than 30 investment companies
                      with more than 95 distinct investment portfolios and total
                      assets in excess of $360 billion. The Vanguard Group, Inc.
                      ("Vanguard"), a subsidiary jointly owned by the Vanguard
                      Funds, provides all corporate management, administrative,
                      distribution, and shareholder accounting services on an
                      at-cost basis to the Funds in the Group. As a result,
                      Vanguard's operating expenses are substantially lower than
                      those of the mutual fund industry.                 PAGE 17
    
- --------------------------------------------------------------------------------
 
INVESTMENT
ADVISER               Vanguard's Fixed Income Group provides investment advisory
                      services on an at-cost basis to the Fund's four
                      Portfolios.                                        PAGE 17
- --------------------------------------------------------------------------------
 
DIVIDENDS, CAPITAL
GAINS AND TAXES       Each Portfolio declares a dividend each business day based
                      on its ordinary income. Dividends are paid on the first
                      business day of each month. Net capital gains, if any,
                      will be distributed annually. Each Portfolio's dividend
                      and capital gains distributions are automatically
                      reinvested in additional shares.
 
   
                      If you utilize any of the Fund's Portfolios as an
                      investment option in an employer-sponsored retirement
                      savings plan, dividend and capital gains distributions
                      from the Portfolios will generally not be subject to
                      current taxation, but will accumulate on a tax-deferred
                      basis.                                             PAGE 19
    
- --------------------------------------------------------------------------------
 
SPECIAL
CONSIDERATIONS        (1) Each Portfolio may invest a portion of its assets in
                          bond (interest rate) futures contracts and options.
 
                      (2) Each Portfolio may lend its securities.        PAGE 15
- --------------------------------------------------------------------------------
 
                                        3
<PAGE>   43
 
FUND EXPENSES         The following tables illustrate ALL expenses and fees that
                      you would incur as a shareholder of the Fund. The expenses
                      and fees set forth in the table are for the 1997 fiscal
                      year.
 
<TABLE>
<CAPTION>
                                                                  TOTAL BOND   SHORT-TERM   INTERMEDIATE-   LONG-TERM
                                          SHAREHOLDER               MARKET        BOND        TERM BOND       BOND
                                     TRANSACTION EXPENSES         PORTFOLIO    PORTFOLIO      PORTFOLIO     PORTFOLIO
                               --------------------------------------------------------------------------------------
                               <S>                                <C>          <C>          <C>             <C>
                               Sales Load Imposed on
                                 Purchases*.....................    None         None          None           None
                               Sales Load Imposed on
                                 Reinvested Dividends...........    None         None          None           None
                               Redemption Fees**................    None         None          None           None
                               Exchange Fees....................    None         None          None           None
                                * The Fund reserves the right to deduct a portfolio transaction fee, ranging from
                                  0.15% to 0.25% and payable directly to the Portfolio, from purchases of a size that
                                  is reasonably deemed to be disruptive to efficient portfolio management. See text
                                  below.
                               ** Wire redemptions of less than $5,000 are subject to a $5 processing fee.
</TABLE>
 
<TABLE>
<CAPTION>
                                                                 TOTAL BOND   SHORT-TERM   INTERMEDIATE-   LONG-TERM
                                         ANNUAL FUND               MARKET        BOND        TERM BOND       BOND
                                      OPERATING EXPENSES         PORTFOLIO    PORTFOLIO      PORTFOLIO     PORTFOLIO
                               -------------------------------------------------------------------------------------
                               <S>                               <C>          <C>          <C>             <C>
                               Management & Administrative
                                 Expenses......................     0.14%        0.14%         0.14%         0.11%
                               Investment Advisory Fees........     0.01         0.01          0.01          0.01
                               12b-1 Fees......................     None         None          None          None
                               Other Expenses
                                   Distribution Costs..........     0.03         0.03          0.03          0.03
                                   Miscellaneous Expenses......     0.02         0.02          0.02          0.05
                                                                 -------      -------      ---------       -------
                               Total Other Expenses............     0.05         0.05          0.05          0.08
                                                                 -------      -------      ---------       -------
                                        TOTAL OPERATING
                                          EXPENSES.............     0.20%        0.20%         0.20%         0.20%
                                                                 =======      =======      =========       =======
</TABLE>
 
   
                      The purpose of these tables is to assist you in
                      understanding the various costs and expenses that you
                      would bear directly or indirectly as an investor in the
                      Fund.
    
 
TRANSACTION FEE       The Fund reserves the right to deduct a portfolio
                      transaction fee from purchases of the shares of each
                      Portfolio. Fees will not be charged on any investment
                      where the aggregate balance is expected to be less than
                      $50 million for the Total Bond Market Portfolio; $15
                      million for the Short-Term Bond Portfolio; $15 million for
                      the Intermediate-Term Bond Portfolio; and $2 million for
                      the Long-Term Bond Portfolio. Fees may be charged on the
                      entire lump-sum purchase for transactions that exceed or
                      are expected to exceed the amount indicated for each
                      Portfolio over the next twelve months, if such purchases
                      are reasonably deemed to be disruptive to efficient
                      portfolio management. Lump-sum purchases exceeding the
                      indicated amount for each Portfolio may be considered
                      disruptive, for example, if the portfolio manager incurs
                      significant transaction costs in purchasing portfolio
                      securities needed to match the investment performance of
                      the respective benchmark index. If such purchases can be
                      offset by redemptions of shares by other shareholders,
                      such fee may be waived or reduced. A prospective investor
                      may determine whether a fee will be charged by calling
                      his/her client representative or plan sponsor in advance
                      of his/her purchase. The fee, if imposed, will be 0.18%
                      for the Total Bond Market
 
                                        4
<PAGE>   44
 
                      Portfolio; 0.23% for the Intermediate-Term Bond Portfolio;
                      0.15% for the Short-Term Bond Portfolio; and 0.20% for the
                      Long-Term Bond Portfolio. The fees are based on the
                      portfolio manager's estimate of transaction costs, which
                      depends on the types of securities in which each Portfolio
                      invests.
 
                      The following example illustrates the expenses that you
                      would incur on a $1,000 investment over various periods,
                      assuming (1) a 5% annual rate of return and (2) redemption
                      at the end of each period. As noted in the table on page
                      4, the Portfolios charge no redemption fees of any kind.
 
<TABLE>
<CAPTION>
                                                                           1 YEAR   3 YEARS   5 YEARS   10 YEARS
                                                                           ------   -------   -------   --------
                               <S>                                         <C>      <C>       <C>       <C>
                               Total Bond Market Portfolio...............    $2       $6        $11       $26
                               Short-Term Bond Portfolio.................    $2       $6        $11       $26
                               Intermediate-Term Bond Portfolio..........    $2       $6        $11       $26
                               Long-Term Bond Portfolio..................    $2       $6        $11       $26
</TABLE>
 
                      THIS EXAMPLE SHOULD NOT BE CONSIDERED A REPRESENTATION OF
                      PAST OR FUTURE EXPENSES OR PERFORMANCE. ACTUAL EXPENSES
                      MAY BE HIGHER OR LOWER THAN THOSE SHOWN.
- --------------------------------------------------------------------------------
 
FINANCIAL
HIGHLIGHTS            The following financial highlights information with
                      respect to the Total Bond Market, Short-Term Bond,
                      Intermediate-Term Bond and Long-Term Bond Portfolios, for
                      a share outstanding throughout each period presented, has
                      been derived from financial statements which were audited
                      by Price Waterhouse LLP, independent accountants, whose
                      report thereon was unqualified. This information should be
                      read in conjunction with the Fund's 1997 financial
                      statements and notes thereto, which, together with the
                      remaining portions of the Fund's 1997 Annual Report to
                      Shareholders, are incorporated by reference in the
                      Statement of Additional Information and this Prospectus,
                      and which appear, along with the report of Price
                      Waterhouse LLP, in the Fund's 1997 Annual Report to
                      Shareholders. For a more complete discussion of the Fund's
                      performance, please see the Fund's 1997 Annual Report to
                      Shareholders which may be obtained without charge by
                      writing to the Fund or calling Participant Services at
                      1-800-523-1188.
 
                                        5
<PAGE>   45
 
<TABLE>
<CAPTION>
                                      -------------------------------------------------------------------------------------------
                                                                      TOTAL BOND MARKET PORTFOLIO
                                      -------------------------------------------------------------------------------------------
                                                                        YEAR ENDED DECEMBER 31,
                                      -------------------------------------------------------------------------------------------
                                       1997     1996     1995     1994     1993     1992     1991     1990     1989     1988
- ---------------------------------------------------------------------------------------------------------------------------------
<S>                                   <C>      <C>      <C>      <C>      <C>      <C>      <C>      <C>      <C>      <C>    <C>
NET ASSET VALUE, BEGINNING OF
  PERIOD............................  $ 9.84   $10.14   $ 9.17   $10.06   $ 9.88   $ 9.99   $ 9.41   $ 9.44   $ 9.05   $ 9.20
                                      ------   ------   ------   ------   ------   ------   ------   ------   ------   ------
INVESTMENT OPERATIONS
  Net Investment Income.............    .645     .640     .650     .622     .638     .699     .766     .796     .797     .807
  Net Realized and Unrealized
    Gain (Loss) on Investments......    .250    (.300)    .970    (.888)    .300    (.018)    .605    (.030)    .390    (.150)
                                      ------   ------   ------   ------   ------   ------   ------   ------   ------   ------
      TOTAL FROM INVESTMENT
        OPERATIONS..................    .895     .340    1.620    (.266)    .938     .681    1.371     .766    1.187     .657
- ---------------------------------------------------------------------------------------------------------------------------------
DISTRIBUTIONS
  Dividends from Net Investment
    Income..........................   (.645)   (.640)   (.650)   (.622)   (.638)   (.699)   (.766)   (.796)   (.797)   (.807)
  Distributions from Realized
    Capital Gains...................      --       --       --    (.002)   (.120)   (.092)   (.025)      --       --       --
                                      ------   ------   ------   ------   ------   ------   ------   ------   ------   ------
      TOTAL DISTRIBUTIONS...........   (.645)   (.640)   (.650)   (.624)   (.758)   (.791)   (.791)   (.796)   (.797)   (.807)
- ---------------------------------------------------------------------------------------------------------------------------------
NET ASSET VALUE, END OF PERIOD......  $10.09   $ 9.84   $10.14   $ 9.17   $10.06   $ 9.88   $ 9.99   $ 9.41   $ 9.44   $ 9.05
=================================================================================================================================
TOTAL RETURN (1)....................    9.44%    3.58%   18.18%   (2.66)%   9.68%    7.14%   15.25%    8.65%   13.65%    7.35%
=================================================================================================================================
RATIOS/SUPPLEMENTAL DATA
Net Assets, End of Period
  (Millions)........................  $5,129   $2,962   $2,405   $1,731   $1,540   $1,066     $849     $277     $139      $58
Ratio of Total Expenses to
  Average Net Assets................    0.20%    0.20%    0.20%    0.18%    0.18%    0.20%    0.16%    0.21%    0.24%    0.30%
Ratio of Net Investment Income to
  Average Net Assets................    6.54%    6.54%    6.66%    6.57%    6.24%    7.06%    7.95%    8.60%    8.49%    8.84%
Portfolio Turnover Rate.............      39%      39%      36%      33%      50%      49%      31%      29%      33%      21%
(1) Total return figures do not reflect the annual account maintenance fee of $10 (charged to individual investors).
</TABLE>
 
<TABLE>
<CAPTION>
                                                              -------------------------------------------------
                                                                          SHORT-TERM BOND PORTFOLIO
                                                              -------------------------------------------------
                                                                 YEAR ENDED DECEMBER 31,
                                                              ------------------------------       MAR. 1+ TO
                                                               1997        1996        1995       DEC. 31, 1994
- ---------------------------------------------------------------------------------------------------------------
<S>                                                           <C>         <C>         <C>         <C>
NET ASSET VALUE, BEGINNING OF PERIOD........................  $ 9.92      $10.07      $ 9.50         $10.00
                                                              ------      ------      ------      ----------
INVESTMENT OPERATIONS
  Net Investment Income.....................................    .597        .587        .623           .463
  Net Realized and Unrealized Gain
    (Loss) on Investments...................................    .080       (.146)       .570          (.500)
                                                              ------      ------      ------      ----------
      TOTAL FROM INVESTMENT OPERATIONS......................    .677        .441       1.193          (.037)
- ---------------------------------------------------------------------------------------------------------------
DISTRIBUTIONS
  Dividends from Net Investment Income......................   (.597)      (.587)      (.623)         (.463)
  Distributions from Realized Capital Gains.................      --       (.004)         --             --
                                                              ------      ------      ------      ----------
      TOTAL DISTRIBUTIONS...................................   (.597)      (.591)      (.623)         (.463)
- ---------------------------------------------------------------------------------------------------------------
NET ASSET VALUE, END OF PERIOD..............................  $10.00      $ 9.92      $10.07         $ 9.50
===============================================================================================================
TOTAL RETURN (1)............................................    7.04%       4.55%      12.88%         (0.37)%
===============================================================================================================
RATIOS/SUPPLEMENTAL DATA
Net Assets, End of Period (Millions)........................    $446        $328        $208            $77
Ratio of Total Expenses to Average Net Assets...............    0.20%       0.20%       0.20%          0.18%*
Ratio of Net Investment Income to Average Net Assets........    6.03%       5.93%       6.28%          5.77%*
Portfolio Turnover Rate.....................................      88%++       65%         65%            53%
 * Annualized.
 + Subscription period for the Portfolio was from January 18, 1994, through February 28, 1994, during which
   time all assets were held in money market instruments.
(1) Total return figures do not reflect the annual account maintenance fee of $10 (charged to individual
  investors).
 ++ Portfolio turnover rate excluding in-kind redemptions was 73%.
</TABLE>
 
- --------------------------------------------------------------------------------
 
                                        6
<PAGE>   46
 
<TABLE>
<CAPTION>
                                       ---------------------------------------    -------------------------------------------
                                                  INTERMEDIATE-TERM                                LONG-TERM
                                                   BOND PORTFOLIO                               BOND PORTFOLIO
                                       ---------------------------------------    -------------------------------------------
                                        YEAR ENDED DECEMBER 31,     MAR. 1+ TO     YEAR ENDED DECEMBER 31,     MAR. 1+ TO
                                       --------------------------    DEC. 31,     --------------------------    DEC. 31,
                                        1997      1996      1995       1994        1997      1996      1995       1994
- -----------------------------------------------------------------------------------------------------------------------------
<S>                                    <C>       <C>       <C>      <C>           <C>       <C>       <C>      <C>        <C>
NET ASSET VALUE, BEGINNING OF
  PERIOD.............................  $ 9.96    $10.37    $ 9.18      $10.00     $10.08    $10.82    $ 8.96      $10.00
                                       ------    ------    ------   --------      ------    ------    ------   --------
INVESTMENT OPERATIONS
  Net Investment Income..............    .661      .648      .661       .533        .678      .674      .692       .586
  Net Realized and Unrealized
    Gain (Loss) on Investments.......    .240     (.406)    1.217      (.820)       .700     (.731)    1.884     (1.040)
                                       ------    ------    ------   --------      ------    ------    ------   --------
      TOTAL FROM INVESTMENT
        OPERATIONS...................    .901      .242     1.878      (.287)      1.378     (.057)    2.576      (.454)
- -----------------------------------------------------------------------------------------------------------------------------
DISTRIBUTIONS
  Dividends from Net Investment
    Income...........................   (.661)    (.648)    (.661)     (.533)      (.678)    (.674)    (.692)     (.586)
  Distributions from Realized
    Capital Gains....................      --     (.004)    (.027)        --          --     (.009)    (.024)        --
                                       ------    ------    ------   --------      ------    ------    ------   --------
      TOTAL DISTRIBUTIONS............   (.661)    (.652)    (.688)     (.533)      (.678)    (.683)    (.716)     (.586)
- -----------------------------------------------------------------------------------------------------------------------------
NET ASSET VALUE, END OF PERIOD.......  $10.20    $ 9.96    $10.37      $ 9.18     $10.78    $10.08    $10.82      $ 8.96
=============================================================================================================================
TOTAL RETURN (1).....................    9.41%     2.55%    21.07%     (2.88)%     14.30%    (0.26)%   29.72%     (4.53)%
=============================================================================================================================
RATIOS/SUPPLEMENTAL DATA
Net Assets, End of Period
  (Millions).........................    $687      $460      $346         $71        $88       $44       $24          $9
Ratio of Total Expenses to
  Average Net Assets.................    0.20%     0.20%     0.20%      0.18%*      0.20%     0.20%     0.20%      0.18%*
Ratio of Net Investment Income to
  Average Net Assets.................    6.64%     6.54%     6.55%      6.88%*      6.66%     6.75%     6.90%      7.70%*
Portfolio Turnover Rate..............      56%       80%       71%        63%         58%       46%       45%        70%
 * Annualized.
(1) Total return figures do not reflect the annual account maintenance fee of $10 (charged to individual investors).
 + Subscription period for the Portfolio was from January 18, 1994, through February 28, 1994, during which time all
   assets were held in money market instruments.
</TABLE>
 
- --------------------------------------------------------------------------------
 
YIELD AND
TOTAL RETURN          From time to time each Portfolio may advertise its yield
                      and total return. Both yield and total return figures are
                      based on historical earnings and are not intended to
                      indicate future performance. The "total return" of a
                      Portfolio refers to the average annual compounded rates of
                      return over one-, five- and ten-year periods or for the
                      life of the Portfolio (as stated in the advertisement)
                      that would equate an initial amount invested at the
                      beginning of a stated period to the ending redeemable
                      value of the investment, assuming the reinvestment of all
                      dividend and capital gains distributions.
 
                      In accordance with industry guidelines set forth by the
                      U.S. Securities and Exchange Commission, the "30-day
                      yield" of a Portfolio is calculated by dividing the net
                      investment income per share earned during a 30-day period
                      by the net asset value per share on the last day of the
                      period. Net investment income includes interest and
                      dividend income earned on the Portfolio's securities; it
                      is net of all expenses and all recurring and nonrecurring
                      charges that have been applied to all shareholder
                      accounts. The yield calculation assumes that the net
                      investment income earned over 30 days is compounded
                      monthly for six months and then annualized. Methods used
                      to calculate advertised yields are standardized for all
                      stock and bond mutual funds. However, these methods differ
                      from the accounting methods used by a Portfolio to
                      maintain its books and records, and so the advertised
                      30-day yield may not fully reflect the income paid to an
                      investor's account.
- --------------------------------------------------------------------------------
 
                                        7
<PAGE>   47
 
INVESTMENT
OBJECTIVE
EACH PORTFOLIO
SEEKS TO MATCH
THE INVESTMENT
PERFORMANCE OF ITS
RESPECTIVE INDEX      The Fund is an open-end diversified investment company
                      designed as an "index" fund. The Fund consists of four
                      Portfolios, each of which seeks to match the investment
                      results of a particular investment grade bond index
                      through the use of index sampling techniques. The Total
                      Bond Market Portfolio seeks to replicate the performance
                      of a broad market-weighted bond index, while the
                      Short-Term Bond, Intermediate-Term Bond and Long-Term Bond
                      Portfolios attempt to replicate the performance of
                      market-weighted bond indexes with prescribed maturity
                      standards. There is no assurance that any of the Fund's
                      Portfolios will achieve its stated objective.
 
                      The investment objective of each Portfolio is fundamental
                      and so cannot be changed without the approval of a
                      majority of a Portfolio's shareholders.
- --------------------------------------------------------------------------------
 
INVESTMENT
POLICIES
EACH PORTFOLIO USES A
"PASSIVE" APPROACH
TO INVEST IN FIXED-
INCOME SECURITIES     The four Portfolios of the Fund are not managed according
                      to traditional methods of "active" investment management,
                      which involve the buying and selling of securities based
                      upon economic, financial, and market analyses and
                      investment judgment. Instead, the Portfolios, utilizing a
                      "passive" or "indexing" investment approach, will attempt
                      to duplicate the investment performance of their
                      respective indexes through statistical sampling
                      procedures. Each Portfolio will invest in a group of
                      fixed-income securities selected from its respective index
                      which, when taken together, are expected to perform
                      similarly to the index as a whole. This sampling technique
                      is expected to enable each Portfolio to track the dividend
                      income and price movements of its respective index, while
                      minimizing brokerage, custodial and accounting costs. The
                      Portfolios are managed without regard to tax
                      ramifications.
 
                      The TOTAL BOND MARKET PORTFOLIO will invest in a portfolio
                      of fixed-income securities selected to match the Lehman
                      Brothers Aggregate Bond Index (the "Aggregate Bond
                      Index"). The Aggregate Bond Index is a broad
                      market-weighted index which encompasses four major classes
                      of investment grade fixed-income securities in the United
                      States: U.S. Treasury and agency securities, corporate
                      bonds, international (dollar-denominated) bonds, and
                      mortgage-backed securities, with maturities greater than
                      one year.
 
                      The SHORT-TERM BOND PORTFOLIO will invest in a portfolio
                      of fixed-income securities selected to match the Lehman
                      Brothers Mutual Fund Short (1-5) Government/ Corporate
                      Index (the "Short-Term Index"). The Short-Term Index is a
                      market-weighted index which encompasses three major
                      classes of investment grade fixed-income securities: U.S.
                      Treasury and agency securities, corporate bonds and
                      international (dollar-denominated) bonds, all with
                      maturities between 1 and 5 years.
 
                      The INTERMEDIATE-TERM BOND PORTFOLIO will invest in a
                      portfolio of fixed-income securities selected to match the
                      Lehman Brothers Mutual Fund Intermediate (5-10)
                      Government/Corporate Index (the "Intermediate-Term
                      Index"). The Intermediate-Term Index is a market-weighted
                      index which encompasses three major classes of investment
                      grade fixed-income securities: U.S. Treasury and agency
                      securities,
 
                                        8
<PAGE>   48
 
                      corporate bonds and international (dollar-denominated)
                      bonds, all with maturities between 5 and 10 years.
 
                      The LONG-TERM BOND PORTFOLIO will invest in a portfolio of
                      fixed-income securities selected to match the Lehman
                      Brothers Long (10+) Government/Corporate Index (the
                      "Long-Term Index"). The Long-Term Index is a
                      market-weighted index which encompasses three major
                      classes of investment grade fixed-income securities: U.S.
                      Treasury and agency securities, corporate bonds and
                      international (dollar-denominated) bonds, all with
                      maturities greater than 10 years.
 
                      Each Portfolio will invest 80% or more of its assets in
                      securities included in its respective index. As of
                      December 31, 1997, the major classes of fixed-income
                      securities represented the following proportions of the
                      respective indexes' total market values:
 
<TABLE>
<CAPTION>
                                                            AGGREGATE    SHORT-TERM   INTERMEDIATE-   LONG-TERM
                                                            BOND INDEX     INDEX       TERM INDEX       INDEX
                                                            ----------   ----------   -------------   ---------
                               <S>                          <C>          <C>          <C>             <C>
                               U.S. Treasury and agency
                                 securities                      49%          83%            58%           65%
                               Corporate bonds                   17%          14%            32%           29%
                               International (dollar-
                                 denominated) bonds               4%           3%            10%            6%
                               Mortgage-backed securities        30%           0%             0%            0%
                               Dollar-weighted average
                                 maturity (Years)            8.7 yrs      2.7 yrs        7.4 yrs      23.6 yrs
</TABLE>
 
                      The Portfolios of the Fund may, from time to time,
                      substitute one type of investment grade bond for another.
                      For instance, a Portfolio may hold more short-term
                      corporate bonds (fewer short-term U.S. Treasury bonds)
                      than represented in the Index so as to increase income.
                      This corporate substitution strategy will entail the
                      assumption of additional credit risk; however, substantial
                      diversification within the corporate sector should
                      moderate issue-specific credit risk. In addition, current
                      investment policy restricts corporate substitutions to
                      issues with less than 4 years remaining to maturity and in
                      aggregate no more than 15% of net assets. Overall, credit
                      risk is expected to be very low for each of the
                      Portfolios.
 
                      Fixed-income securities will be primarily of investment
                      grade quality -- i.e., those rated at least Baa3 by
                      Moody's Investors Service, Inc. or BBB- by Standard &
                      Poor's Corporation. Securities rated Baa or BBB are
                      considered as medium grade obligations. Interest payments
                      and principal are regarded as adequate for the present but
                      certain protective elements found in higher rated bonds
                      may be lacking. Such bonds lack outstanding investment
                      characteristics and, in fact, have speculative
                      characteristics as well.
 
                      In its effort to duplicate the investment performance of
                      its Index, each Portfolio will invest in fixed-income
                      securities approximating its relative proportion of the
                      Index's total market value. For the Total Bond Market
                      Portfolio, these investments will
 
                                        9
<PAGE>   49
 
                      include U.S. Treasury and agency securities,
                      mortgage-backed securities and corporate and international
                      (dollar-denominated) bonds. For the Short-Term Bond,
                      Intermediate-Term Bond and Long-Term Bond Portfolios,
                      these investments include U.S. Treasury and agency
                      securities, corporate debt and international (dollar-
                      denominated) debt. The Portfolios may invest in U.S.
                      Treasury bills, notes and bonds and other "full faith and
                      credit" obligations of the U.S. Government. The Portfolios
                      may also invest in U.S. Government agency securities,
                      which are debt obligations issued or guaranteed by
                      agencies or instrumentalities of the U.S. Government. Such
                      "agency" securities may not be backed by the "full faith
                      and credit" of the U.S. Government. Such U.S. Government
                      agencies may include the Federal Farm Credit Banks, the
                      Resolution Trust Corporation and in the case of the Total
                      Bond Market Portfolio, the Government National Mortgage
                      Association. Even though they all carry top (AAA) credit
                      ratings, "agency" obligations are not explicitly
                      guaranteed by the U.S. Government and so are perceived as
                      somewhat riskier than comparable Treasury bonds.
 
                      Each Portfolio may also invest up to 20% of its assets in
                      short-term money market instruments, and may invest in
                      bond (interest rate) futures contracts and options to a
                      limited extent. Such securities will be held only to
                      invest uncommitted cash balances, to maintain liquidity to
                      meet shareholder redemptions, or to minimize trading
                      costs. The Portfolios will not invest in such securities
                      as part of a temporary defensive strategy (such as
                      altering the aggregate maturity of a Portfolio) to protect
                      the Fund against potential bond market declines. Each
                      Portfolio intends to remain fully invested, to the extent
                      practicable, in a pool of securities which will duplicate
                      the investment characteristics of the respective index.
                      See "Implementation of Policies" for a description of
                      other investment practices of the Fund.
 
                      The Fund is responsible for voting the shares of all
                      securities it holds.
 
                      These investment policies are not fundamental and so may
                      be changed by the Board of Directors without shareholder
                      approval. However, shareholders would be notified prior to
                      any material change.
- --------------------------------------------------------------------------------
 
INVESTMENT
RISKS                 As mutual funds investing primarily in fixed-income
                      securities, the Portfolios are subject to interest rate,
                      income, call and credit risks. Since the Total Bond Market
                      Portfolio also invests in mortgage-backed securities, the
                      Portfolio is also subject to prepayment risk.
 
THE PORTFOLIOS ARE
SUBJECT TO INTEREST
RATE RISK             INTEREST RATE RISK is the potential for fluctuations in
                      bond prices due to changing interest rates. As a rule,
                      bond prices vary inversely with interest rates. If
                      interest rates rise, bond prices generally decline; if
                      interest rates fall, bond prices generally rise. In
                      addition, for a given change in interest rates,
                      longer-maturity bonds fluctuate more in price than
                      shorter-maturity bonds. To compensate investors for these
                      larger fluctuations, longer-maturity bonds usually offer
                      higher yields than shorter-maturity bonds, other factors,
                      including credit quality, being equal.
 
                      These basic principles of bond prices also apply to U.S.
                      Government securities. A security backed by the "full
                      faith and credit" of the U.S. Government is guaranteed
 
                                       10
<PAGE>   50
 
                      only as to its stated interest rate and face value at
                      maturity, not its current market price. Just like other
                      fixed-income securities, government-guaranteed securities
                      will fluctuate in value when interest rates change.
 
                      The TOTAL BOND MARKET and INTERMEDIATE-TERM BOND
                      PORTFOLIOS maintain an intermediate-term dollar-weighted
                      average maturity, and are therefore subject to a moderate
                      to high level of interest rate risk. Interest rate risk
                      for the SHORT-TERM BOND PORTFOLIO should be modest.
                      Because of the short-term dollar-weighted average
                      maturities, the Portfolio is expected to exhibit low to
                      moderate price fluctuations as interest rates change. The
                      LONG-TERM BOND PORTFOLIO is exposed to substantial
                      interest rate risk. The Portfolio is expected to have a
                      dollar-weighted average maturity in excess of 15 years
                      which exposes it to high to very high price fluctuations
                      due to changing interest rates.
 
                      As an illustration of interest rate risk, the chart below
                      depicts the effect of a two percentage point change in
                      interest rates on three bonds of varying maturities:
 
                        PERCENTAGE CHANGE IN PRICE OF A PAR BOND YIELDING 7.5%
 
                      ----------------------------------------------------------
 
<TABLE>
<CAPTION>
                                                                    2 PERCENTAGE POINT   2 PERCENTAGE POINT
                                                                       INCREASE IN          DECREASE IN
                                         STATED MATURITY              INTEREST RATES       INTEREST RATES
                               -----------------------------------  ------------------   ------------------
                               <S>                                  <C>                  <C>
                               Short-Term (2.5 years)                     - 4.4%               + 4.6%
                               Intermediate-Term (10 years)               -12.7%               +15.2%
                               Long-Term (20 years)                       -17.8%               +24.1%
</TABLE>
 
                      This chart is intended to provide you with guidelines for
                      determining the degree of interest rate risk you may be
                      willing to assume. The yield and price changes shown
                      should not be taken as representative of a Portfolio's
                      current or future yield or expected changes in a
                      Portfolio's share price.
 
THE PORTFOLIOS ARE
SUBJECT TO INCOME RISKINCOME RISK is the potential for a decline in a
                      Portfolio's income due to falling market interest rates.
                      In relative terms, income risk will be higher for the
                      Fund's shorter-term Portfolios and lower for the Fund's
                      longer-term Portfolios.
 
THE LONG-TERM BOND
PORTFOLIO IS SUBJECT TO
CALL RISK             An additional risk associated with long-term corporate
                      bonds is call risk. CALL RISK is the possibility that
                      corporate bonds held by the Portfolio will be repaid prior
                      to maturity. Call provisions, common in many corporate
                      bonds, allow bond issuers to redeem bonds prior to
                      maturity (at a specific price). When interest rates are
                      falling, bond issuers often exercise these call
                      provisions, paying off bonds that carry high stated
                      interest rates and often issuing new bonds at lower rates.
                      For the Portfolio, the result would be that bonds with
                      high interest rates are "called" and must be replaced with
                      lower-yielding instruments. In these circumstances, the
                      income of the Portfolio would decline. Reflecting these
                      additional credit and call risks, the corporate portion of
                      the portfolio will generally offer higher yields than the
                      government portion.
 
                                       11
<PAGE>   51
 
THE TOTAL BOND
MARKET PORTFOLIO
IS SUBJECT TO
PREPAYMENT RISK       As a mutual fund investing a portion of its assets in
                      mortgage-backed securities (see chart on page 9), the
                      Total Bond Market Portfolio is subject to prepayment risk
                      to a limited extent. PREPAYMENT RISK is the possibility
                      that, during periods of declining interest rates, the
                      principal invested in high-yielding mortgage-backed
                      securities will be repaid earlier than scheduled, and the
                      Fund will be forced to reinvest the unanticipated payments
                      at generally lower interest rates.
 
                      Prepayment risk has two important effects on the
                      Portfolio. First, when interest rates fall and principal
                      prepayments are reinvested at lower interest rates, the
                      income that the Portfolio derives from mortgage-backed
                      securities is reduced. Second, like other fixed-income
                      securities, mortgage-backed securities generally decline
                      in price when interest rates rise. However, because of
                      prepayment risk, mortgage-backed securities (and thus in
                      part the share price of the Portfolio and the value of the
                      Index) will not enjoy as large a gain in market value as
                      ordinary bonds when interest rates fall. In part to
                      compensate for prepayment risk, mortgage-backed securities
                      generally offer higher yields than bonds of comparable
                      credit quality and maturity.
 
CREDIT RISK IS EXPECTED
TO BE LOW             CREDIT RISK is the possibility that an issuer of
                      securities held by a Portfolio will be unable to make
                      payments of either interest or principal. The credit risk
                      of a Portfolio is a function of the credit quality of its
                      underlying securities.
 
                      The credit quality of each Portfolio is expected to be
                      very high, and thus credit risk should be low. As of
                      December 31, 1997, the average quality, as rated by
                      Moody's Investors Service, Inc., of each Portfolio's
                      benchmark index was as follows:
 
<TABLE>
                               <S>                                                           <C>
                               Aggregate Bond Index........................................  Aaa
                               Short-Term Bond Index.......................................  Aaa
                               Intermediate-Term Bond Index................................  Aa1
                               Long-Term Bond Index........................................  Aa2
</TABLE>
 
                      To a limited extent, the Portfolios are also exposed to
                      EVENT RISK, the possibility that corporate fixed-income
                      securities held by the Portfolios may suffer a substantial
                      decline in credit quality and market value due to a
                      corporate restructuring. Corporate restructurings, such as
                      mergers, leveraged buyouts, takeovers or similar events,
                      are often financed by a significant expansion of corporate
                      debt. As a result of the added debt burden, the credit
                      quality and market value of a firm's existing debt
                      securities may decline significantly. While event risk may
                      be high for certain corporate and international
                      (dollar-denominated) securities held by the Portfolios,
                      event risk for each Portfolio in the aggregate should be
                      low because of each Portfolio's diversified holdings and
                      the small percentage of Portfolio assets invested in these
                      securities.
 
                      The corporate substitution strategy will increase credit
                      risk somewhat, as short-term investment grade corporate
                      bonds are substituted for U.S. Treasury bonds and notes;
                      however, owing to the diversified nature of the
                      Portfolios, and policies limiting the maturity and maximum
                      amount of substitutions, the overall credit and event risk
                      of the Portfolios is expected to be low.
 
                                       12
<PAGE>   52
 
NO CURRENCY RISK
IN ANY PORTFOLIO
                      While each of the chosen Lehman Index benchmarks do have
                      limited exposure to international bonds, there is no
                      currency risk associated with the investments since they
                      are all dollar-denominated.
- --------------------------------------------------------------------------------
 
WHO SHOULD
INVEST
INVESTORS SEEKING TO
PARTICIPATE IN THE
"BOND MARKET" AS A
WHOLE OR ITS VARIOUS
MATURITY SEGMENTS     The Portfolios are designed for individual and
                      institutional investors seeking well-diversified, low-cost
                      ways to participate in the U.S. fixed-income markets. The
                      Portfolios will be essentially fully invested at all
                      times. Because the Total Bond Market Portfolio will
                      represent all major sectors of the investment grade fixed-
                      income securities market, the Portfolio is a suitable
                      vehicle for those investors seeking ownership in the "bond
                      market" as a whole, without regard to particular sectors.
                      The Short-Term Bond, Intermediate-Term Bond and Long-Term
                      Bond Portfolios are suitable vehicles for those investors
                      seeking ownership in specific maturity segments of the
                      "bond market." Each Portfolio concentrates on bonds of
                      various maturities as illustrated in the chart on page 9.
                      Because of the risks associated with bond investments,
                      each Portfolio is intended to be a long-term investment
                      vehicle and is not designed to provide investors with a
                      means of speculating on short-term bond market movements.
 
   
                      As with all longer-term, fixed-income investments, the
                      share price of the Total Bond Market, Intermediate-Term
                      Bond and Long-Term Bond Portfolios will vary, with the
                      Long-Term Bond Portfolio expected to exhibit the greatest
                      volatility. Share price volatility should be significantly
                      less for the Short-Term Bond Portfolio. Credit risk should
                      be minimal for each Portfolio. The investment risks are
                      described beginning on page 10.
    
 
                      The Portfolios are also suitable for those investors with
                      existing common stock holdings who are seeking a
                      complementary fixed-income investment to create a more
                      balanced asset mix.
- --------------------------------------------------------------------------------
 
IMPLEMENTATION
OF POLICIES           The Portfolios follow a variety of investment practices in
                      an effort to duplicate the total return of their
                      respective indexes.
 
THE PORTFOLIOS INVEST
IN FIXED INCOME
SECURITIES            Each Portfolio will invest at least 80% or more of its
                      assets in securities included in its benchmark index. The
                      indexes measure the total investment return (capital
                      change plus income) provided by a universe of fixed-income
                      securities, weighted by the market value outstanding of
                      each security. The securities included in each index
                      generally meet the following criteria, as defined by
                      Lehman Brothers: an outstanding market value of at least
                      $100 million; and investment grade quality -- i.e., rated
                      a minimum of Baa3 by Moody's Investors Service, Inc. The
                      maturities of securities included in each index will vary
                      as described on page 8. If a security held in the Fund's
                      portfolio is downgraded to a rating below these minimum
                      standards, the Fund may continue to hold it until such
                      time as the adviser deems it most advantageous to dispose
                      of the security.
 
THE PORTFOLIOS USE A
"SAMPLING" TECHNIQUE  The Portfolios will be unable to hold all of the
                      individual issues which comprise the indexes because of
                      the large number of securities involved. Instead, each
                      Portfolio will hold a representative sample of the
                      securities in its respective index, selecting a few issues
                      to represent entire "classes" or types of securities in
                      the index. Each
 
                                       13
<PAGE>   53
 
                      Portfolio will be constructed so as to approximately match
                      the composition of its benchmark index as described on
                      pages 8 and 9 after adjusting for the corporate
                      substitution policy described on page 9. The corporate
                      substitution strategy only applies to the Total Bond
                      Market Portfolio and the Short-Term Bond Portfolio.
 
                      At the broadest level, and adjusted for the corporate
                      substitution strategy, each Portfolio will seek to hold
                      securities which reflect the weighting of the major asset
                      classes in its respective index. For the Total Bond Market
                      Portfolio, these classes include U.S. Treasury and agency
                      securities, corporate bonds, and mortgage-backed
                      securities. For the Short-Term Bond, Intermediate-Term
                      Bond and Long-Term Bond Portfolios, the two major classes
                      of securities include U.S. Treasury and agency securities
                      and corporate bonds. For example, if U.S. Treasury and
                      agency securities represent approximately 60% of an
                      index's interest rate risk, then approximately 60% of the
                      respective Portfolio's interest rate risk will come from
                      such securities. Similarly, if corporate bonds represent
                      20% of the interest rate risk of an index, then they will
                      represent approximately 20% of the interest rate risk of
                      the Portfolio.
 
                      Such a sampling technique is expected to be an effective
                      means of substantially duplicating the income and capital
                      returns provided by each index. Over time, the correlation
                      between the performance of a Portfolio and its respective
                      index is expected to be 0.95 or higher. A correlation of
                      1.00 would indicate perfect correlation, which would be
                      achieved when the net asset value of a Portfolio,
                      including the value of its dividend and capital gains
                      distributions, increases or decreases in exact proportion
                      to changes in the index. The performance and structure of
                      a Portfolio versus that of its respective index is
                      monitored regularly. If significant structural mismatches
                      develop, the Portfolio is rebalanced to bring it in line
                      with the index.
 
THE TOTAL BOND
MARKET PORTFOLIO
MAY INVEST IN
MORTGAGE-BACKED
SECURITIES            As part of its effort to duplicate the investment
                      performance of its Index, the Total Bond Market Portfolio
                      may invest in mortgage-backed securities. Mortgage-backed
                      securities represent an interest in an underlying pool of
                      mortgages. Unlike ordinary fixed-income securities, which
                      generally pay a fixed rate of interest and return
                      principal upon maturity, mortgage-backed securities repay
                      both interest income and principal as part of their
                      periodic payments. Because the mortgages underlying
                      mortgage-backed certificates can be prepaid at any time by
                      homeowners or corporate borrowers, mortgage-backed
                      securities give rise to certain unique "prepayment" risks.
                      See "Investment Risks."
 
                      The Total Bond Market Portfolio may purchase
                      mortgage-backed securities issued by the Government
                      National Mortgage Association (GNMA), the Federal Home
                      Loan Mortgage Corporation (FHLMC), the Federal National
                      Mortgage Association (FNMA), and the Federal Housing
                      Authority (FHA). GNMA securities are guaranteed by the
                      U.S. Government as to the timely payment of principal and
                      interest; securities from other Government-sponsored
                      entities are generally not secured by an explicit pledge
                      of the U.S. Government. The Portfolio may also invest in
                      conventional mortgage securities, which are packaged by
                      private corporations and are not guaranteed by the U.S.
                      Government. Mortgage securities that are guaran-
 
                                       14
<PAGE>   54
 
                      teed by the U.S. Government are guaranteed only as to the
                      timely payment of principal and interest. The market value
                      of such securities is not guaranteed and may fluctuate.
 
EACH PORTFOLIO MAY
INVEST IN SHORT-TERM
MONEY MARKET
INSTRUMENTS           Although they normally seek to remain substantially fully
                      invested in securities in the respective indexes, each
                      Portfolio may invest temporarily in certain short-term
                      money market instruments. Such securities may be used to
                      invest uncommitted cash balances or to maintain liquidity
                      to meet shareholder redemptions. These securities include:
                      obligations of the United States Government and its
                      agencies or instrumentalities; commercial paper, bank
                      certificates of deposit, and bankers' acceptances; and
                      repurchase agreements collateralized by these securities.
 
EACH PORTFOLIO MAY
LEND ITS SECURITIES   Each Portfolio may lend its investment securities to
                      qualified institutional investors for either short-term or
                      long-term purposes of realizing additional income. Loans
                      of securities by a Portfolio will be collateralized by
                      cash, letters of credit, or securities issued or
                      guaranteed by the U.S. Government or its agencies. The
                      collateral will equal at least 100% of the current market
                      value of the loaned securities.
 
PORTFOLIO TURNOVER
IS NOT EXPECTED TO
EXCEED 50%            Although it generally seeks to invest for the long term,
                      each Portfolio retains the right to sell securities
                      irrespective of how long they have been held. It is
                      anticipated that the annual portfolio turnover of each
                      Portfolio will not exceed 50%. A turnover rate of 50%
                      would occur, for example, if one half of the securities of
                      a Portfolio were replaced within one year. A portfolio
                      turnover rate of 100% may be considered high for a bond
                      index fund and would result in additional expenses.
 
DERIVATIVE
INVESTING             Derivatives are instruments whose values are linked to or
                      derived from an underlying security or index. The most
                      common and conventional types of derivative securities are
                      futures and options.
 
EACH PORTFOLIO MAY
INVEST IN DERIVATIVE
SECURITIES            Each Portfolio may invest in futures contracts and
                      options, but only to a limited extent. Specifically, a
                      Portfolio of the Fund may enter into futures contracts
                      provided that not more than 5% of its assets are required
                      as a futures contact deposit; in addition, a Portfolio may
                      enter into futures contracts and options transactions only
                      to the extent that obligations under such contracts or
                      transactions represent not more than 20% of the
                      Portfolio's assets.
 
                      Futures contracts and options may be used for several
                      common fund management strategies: to maintain cash
                      reserves while simulating full investment, to facilitate
                      trading, to reduce transaction costs, or to seek higher
                      investment returns when a specific futures contract is
                      priced more attractively than other futures contracts or
                      the underlying security or index.
 
                      The Portfolios may use futures contracts for bona fide
                      "hedging" purposes. In executing a hedge, a manager sells,
                      for example, stock index futures to protect against a
                      decline in the stock market. As such, if the market drops,
                      the value of the futures position will rise, thereby
                      offsetting the decline in value of the Portfolios' stock
                      holdings.
 
                      The Fund may also invest in other conventional derivatives
                      designed to replicate the risk/return characteristics of a
                      conventional fixed income note or bond. Such
 
                                       15
<PAGE>   55
 
                      derivatives would be managed, in both structure and
                      concentration, to adhere to the Fund's investment policy
                      restrictions as to market and credit risk.
 
EACH PORTFOLIO MAY
INVEST IN CMOS        The Portfolios may invest in a relatively conservative
                      class of collateralized mortgage obligations (CMOs) which
                      feature a high degree of cash flow predictability and less
                      vulnerability to mortgage prepayment risk. To reduce
                      credit risk, Vanguard purchases these less risky classes
                      of collateralized mortgage obligations issued only by
                      agencies of the U.S. Government or privately-issued
                      collateralized mortgage obligations that carry
                      high-quality investment-grade ratings.
 
FUTURES CONTRACTS
AND OPTIONS POSE
CERTAIN RISKS         The primary risks associated with the use of futures
                      contracts and options are: (i) imperfect correlation
                      between the change in market value of the bonds held by a
                      Portfolio and the prices of futures contracts and options,
                      and (ii) possible lack of a liquid secondary market for a
                      futures contract and the resulting inability to close a
                      futures position prior to its maturity date. The risk of
                      imperfect correlation will be minimized by investing in
                      those contracts whose price fluctuations are expected to
                      resemble those of the Portfolio's underlying securities.
                      The risk that a Portfolio will be unable to close out a
                      futures position will be minimized by entering into such
                      transactions on a national exchange with an active and
                      liquid secondary market.
 
                      The risk of loss in trading futures contracts in some
                      strategies can be substantial, due both to the low margin
                      deposits required and the extremely high degree of
                      leverage involved in futures pricing. As a result, a
                      relatively small price movement in a futures contract may
                      result in immediate and substantial loss (or gain) to the
                      investor. When investing in futures contracts, a Portfolio
                      will segregate cash or other liquid portfolio securities
                      in the amount of the underlying obligation.
- --------------------------------------------------------------------------------
 
INVESTMENT
LIMITATIONS
EACH PORTFOLIO HAS
ADOPTED CERTAIN
FUNDAMENTAL
LIMITATIONS           Each Portfolio has adopted limitations on some of its
                      investment policies. Some of these limitations are that
                      the Portfolio will not:
 
                      (a) invest more than 5% of its assets in the securities of
                          any single issuer except obligations of the United
                          States Government or government agencies;
                      (b) purchase more than 5% of the voting securities of any
                          issuer;
                      (c) borrow money, except that each Portfolio may borrow
                          from banks (or through reverse repurchase agreements),
                          for temporary or emergency (not leveraging) purposes,
                          including the meeting of redemption requests which
                          might otherwise require the untimely disposition of
                          securities, in an amount not exceeding 15% of the
                          value of a Portfolio's net assets (including the
                          amount borrowed and the value of any outstanding
                          reverse repurchase agreements) at the time the
                          borrowing is made. Whenever borrowings exceed 5% of
                          the value of a Portfolio's net assets, the Portfolio
                          will not make any additional investments;
                      (d) pledge, mortgage or hypothecate its assets to an
                          extent greater than 5% of the value of its total
                          assets; and
                      (e) invest more than 25% of its assets in any one
                          industry.
 
                      A complete list of each Portfolio's investment limitations
                      can be found in the Statement of Additional Information.
                      These limitations are fundamental and may be changed only
                      by approval of a majority of the Portfolio's shareholders.
- --------------------------------------------------------------------------------
 
                                       16
<PAGE>   56
 
   
MANAGEMENT
OF THE FUND
VANGUARD ADMINISTERS
AND DISTRIBUTES THE
FUND                  The Fund is a member of The Vanguard Group of Investment
                      Companies, a family of more than 30 investment companies
                      with more than 95 distinct portfolios and total assets in
                      excess of $360 billion. Through their jointly-owned
                      subsidiary, The Vanguard Group, Inc. ("Vanguard"), the
                      Fund and the other funds in the Group obtain at cost
                      virtually all of their corporate management,
                      administrative, shareholder accounting and distribution
                      services. Vanguard also provides investment advisory
                      services on an at-cost basis to certain Vanguard funds. As
                      a result of Vanguard's unique corporate structure, the
                      Vanguard funds have costs substantially lower than those
                      of most competing mutual funds. In 1997, the average
                      expense ratio (annual costs including advisory fees
                      divided by total net assets) for the Vanguard funds
                      amounted to approximately .28% compared to an average of
                      1.24% for the mutual fund industry (data provided by
                      Lipper Analytical Services).
    
 
                      The Officers of the Fund manage its day-to-day operations
                      and are responsible to the Fund's Board of Directors. The
                      Directors set broad policies for the Fund and choose its
                      Officers. A list of the Directors and Officers of the Fund
                      and a statement of their present positions and principal
                      occupations during the past five years can be found in the
                      Statement of Additional Information.
 
                      Vanguard employs a supporting staff of management and
                      administrative personnel to provide the requisite services
                      to the funds and also furnishes the funds with necessary
                      office space, furnishings and equipment. Each fund pays
                      its share of Vanguard's net expenses, which are allocated
                      among the funds under methods approved by the Board of
                      Directors (Trustees) of each fund. In addition, each fund
                      bears its own direct expenses, such as legal, auditing and
                      custodian fees.
 
                      Vanguard also provides distribution and marketing services
                      to the Vanguard funds. The funds are available on a
                      no-load basis (i.e., there are no sales commissions or
                      12b-1 fees). However, each fund bears its share of the
                      Group's distribution costs.
- --------------------------------------------------------------------------------
 
   
INVESTMENT
ADVISER
VANGUARD MANAGES
THE FUND'S
INVESTMENTS           Each Portfolio receives all investment advisory services
                      from Vanguard's Fixed Income Group. The Fixed Income Group
                      provides investment advisory services to more than 40
                      Vanguard money market and bond portfolios, both taxable
                      and tax-exempt. Total assets under management by
                      Vanguard's Fixed Income Group were more than $100 billion
                      as of December 31, 1997. The Portfolios are not actively
                      managed, but are instead administered by the Fixed Income
                      Group using computerized, quantitative techniques. The
                      Fixed Income Group is supervised by the Officers of the
                      Fund. Ian A. MacKinnon, Managing Director of Vanguard, has
                      been in charge of the Group since its inception in 1981.
    
 
                      Mr. MacKinnon is responsible for setting the broad
                      investment strategies employed by the Fund, and for
                      overseeing the portfolio manager who implements these
                      strategies on a day-to-day basis.
 
                      The Fund's portfolio manager is Kenneth E. Volpert, a
                      Principal of Vanguard, who also serves as portfolio
                      manager of the Vanguard Variable Insurance Fund -- High-
                      Grade Bond Portfolio and the bond portion of the Vanguard
                      Balanced Index Fund. Mr. Volpert began managing the
                      Vanguard Bond Index Fund in December, 1992. For
 
                                       17
<PAGE>   57
 
                      six years prior to joining Vanguard, Mr. Volpert was
                      associated with Mellon Bond Associates.
 
                      The Fixed Income Group places all orders for purchases and
                      sales of portfolio securities. Purchases of portfolio
                      securities are made either directly from the issuer or
                      from securities dealers. The Fixed Income Group may sell
                      portfolio securities prior to their maturity if
                      circumstances and considerations warrant and if it
                      believes such dispositions advisable. The Group seeks to
                      obtain the best available net price and most favorable
                      execution for all portfolio transactions. When the
                      Portfolio purchases a newly issued security at a fixed
                      price, the Group may designate certain members of the
                      underwriting syndicate to receive compensation associated
                      with that transaction. Certain dealers have agreed to
                      rebate a portion of such compensation directly to the
                      Portfolio to offset its management expenses.
- --------------------------------------------------------------------------------
 
PERFORMANCE
RECORD                The tables in this section provide investment results for
                      the Total Bond Market, Short-Term Bond, Intermediate-Term
                      Bond and Long-Term Bond Portfolios for several periods
                      throughout the Fund's lifetime. The results shown
                      represent "total return" investment performance, which
                      assumes the reinvestment of all capital gains and income
                      dividends for the indicated periods. Also included is
                      comparative information with respect to the unmanaged
                      Aggregate Bond Index described on page 8, the Consumer
                      Price Index, a statistical measure of changes in the
                      prices of goods and services, the Lehman Mutual Fund
                      Short-Term (1-5) Government/Corporate Bond Index, the
                      Lehman Mutual Fund Intermediate (5-10)
                      Government/Corporate Bond Index, and the Lehman Long (10+)
                      Government/Corporate Bond Index.
 
   
                      The results shown should not be considered a
                      representation of the total return from an investment made
                      in a Portfolio today. This information is provided to help
                      investors better understand the Portfolios and may not
                      provide a basis for comparison with other investments or
                      mutual funds which use a different method to calculate
                      performance.
    
 
                                   AVERAGE ANNUAL TOTAL RETURN FOR
                       VANGUARD BOND INDEX FUND -- TOTAL BOND MARKET PORTFOLIO
 
                      ----------------------------------------------------------
 
<TABLE>
<CAPTION>
                               FISCAL PERIODS      TOTAL BOND      AGGREGATE     CONSUMER
                               ENDED 12/31/97   MARKET PORTFOLIO   BOND INDEX   PRICE INDEX
                               --------------   ----------------   ----------   -----------
                               <S>              <C>                <C>          <C>
                               1 Year                  9.44%           9.65%        1.70%
                               3 Years                10.24           10.42         2.52
                               5 Years                 7.42            7.48         2.60
                               10 Years                8.88            9.18         3.41
                               Lifetime*               8.09            8.51         3.51
                               * December 11, 1986 to December 31, 1997.
</TABLE>
 
                                       18
<PAGE>   58
 
                                   AVERAGE ANNUAL TOTAL RETURN FOR
                        VANGUARD BOND INDEX FUND -- SHORT-TERM BOND PORTFOLIO
 
                      ----------------------------------------------------------
 
<TABLE>
<CAPTION>
                                                                  LEHMAN MUTUAL FUND
                                                                     SHORT (1-5)
                               FISCAL PERIODS     SHORT-TERM         GOVERNMENT/         CONSUMER
                               ENDED 12/31/97   BOND PORTFOLIO   CORPORATE BOND INDEX   PRICE INDEX
                               --------------   --------------   --------------------   -----------
                               <S>              <C>              <C>                    <C>
                               1 Year                7.04%               7.13%             1.70%
                               3 Years               8.10                8.17              2.52
                               Lifetime*             6.18                6.28              2.50
                               * March 1, 1994 to December 31, 1997.
</TABLE>
 
                                   AVERAGE ANNUAL TOTAL RETURN FOR
                          VANGUARD BOND INDEX FUND -- INTERMEDIATE-TERM BOND
                                              PORTFOLIO
 
                      ----------------------------------------------------------
 
<TABLE>
<CAPTION>
                                                                     LEHMAN MUTUAL FUND
                                                                    INTERMEDIATE (5-10)
                               FISCAL PERIODS   INTERMEDIATE-TERM       GOVERNMENT/         CONSUMER
                               ENDED 12/31/97    BOND PORTFOLIO     CORPORATE BOND INDEX   PRICE INDEX
                               --------------   -----------------   --------------------   -----------
                               <S>              <C>                 <C>                    <C>
                               1 Year                  9.41%                9.43%              1.70%
                               3 Years                10.75                10.92               2.52
                               Lifetime*               7.49                 7.60               2.50
                               * March 1, 1994 to December 31, 1997.
</TABLE>
 
                                   AVERAGE ANNUAL TOTAL RETURN FOR
                         VANGUARD BOND INDEX FUND -- LONG-TERM BOND PORTFOLIO
 
                      ----------------------------------------------------------
 
<TABLE>
<CAPTION>
                                                                  LEHMAN LONG (10+)
                               FISCAL PERIODS     LONG-TERM          GOVERNMENT/         CONSUMER
                               ENDED 12/31/97   BOND PORTFOLIO   CORPORATE BOND INDEX   PRICE INDEX
                               --------------   --------------   --------------------   -----------
                               <S>              <C>              <C>                    <C>
                               1 Year                14.30%             14.52%              1.70%
                               3 Years               13.93              14.22               2.52
                               Lifetime*              9.41               9.59               2.50
                               * March 1, 1994 to December 31, 1997.
</TABLE>
 
- --------------------------------------------------------------------------------
 
DIVIDENDS,
CAPITAL GAINS
AND TAXES
EACH PORTFOLIO PAYS
MONTHLY DIVIDENDS     Dividends consisting of virtually all of the ordinary
                      income of each Portfolio are declared daily and are
                      payable to shareholders of record at the time of
                      declaration. Such dividends are paid on the first business
                      day of each month. Capital gains distributions, if any,
                      are made annually. In addition, each Portfolio may
                      occasionally be required to make supplemental dividend or
                      capital gains distributions at some other time during the
                      year. Each Portfolio's dividend and capital gains
                      distributions are automatically reinvested in additional
                      shares. The Fund intends to continue to qualify as a
                      "regulated investment company" under the Internal Revenue
                      Code so that it will not be subject to federal income tax
                      to the extent that its income is distributed to its
                      shareholders.
 
                      If you utilize the Fund's Portfolios as an investment
                      option in an employer-sponsored retirement savings plan,
                      dividend and capital gains distributions from the
                      Portfolios will generally not be subject to current
                      taxation, but will accumulate
 
                                       19
<PAGE>   59
 
                      on a tax-deferred basis. In general, employer-sponsored
                      retirement and savings plans are governed by a complex set
                      of tax rules. If you participate in such a plan, consult
                      your plan administrator, your plan's Summary Plan
                      Description, or a professional tax adviser regarding the
                      tax consequences of your participation in the plan and of
                      any plan contributions or withdrawals.
- --------------------------------------------------------------------------------
 
THE SHARE PRICE OF
EACH PORTFOLIO        Each Portfolio's share price, or "net asset value" per
                      share, is calculated by dividing the total assets of the
                      Portfolio, less all liabilities, by the total number of
                      shares outstanding, except for the Total Bond Portfolio
                      whereby net asset value is calculated by dividing the net
                      assets attributed to each share class by the total number
                      of shares outstanding for that share class. The net asset
                      value is determined as of the close of trading on the New
                      York Stock Exchange (the "Exchange"), generally 4:00 p.m.
                      Eastern time, on each day that the Exchange is open for
                      trading.
 
                      Short term instruments (those with remaining maturities of
                      60 days or less) may be valued at cost, plus or minus any
                      amortized discount or premium, which approximates market
                      value.
 
                      Bonds and other fixed income securities may be valued on
                      the basis of prices provided by a pricing service when
                      such prices are believed to reflect the fair market value
                      of such securities. The prices provided by a pricing
                      service may be determined without regard to bid or last
                      sale prices of each security, but take into account
                      institutional-size transactions in similar groups of
                      securities as well as any developments related to specific
                      securities.
 
                      Other assets and securities for which no quotations are
                      readily available or which are restricted as to sale (or
                      resale) are valued by such methods as the Board of
                      Directors deems in good faith to reflect fair value.
 
   
                      The share price for each Portfolio of the Fund can be
                      found daily in the mutual fund listings of most major
                      newspapers under the heading of Vanguard Index Funds.
    
- --------------------------------------------------------------------------------
 
GENERAL
INFORMATION           The Fund is a Maryland corporation. The Articles of
                      Incorporation permit the Directors to issue 2,000,000,000
                      shares of common stock, with a $.001 par value. The Board
                      of Directors has the power to designate one or more
                      portfolios and classes of shares of common stock of such
                      portfolios and to classify or reclassify any unissued
                      shares with respect to such portfolios and classes.
                      Currently the Fund is offering shares of four series. The
                      Total Bond Market Portfolio offers two separate classes of
                      shares; the Total Bond Market Portfolio Investor Shares
                      which is open to investors with a minimum investment of
                      $3,000, and the Total Bond Market Portfolio Institutional
                      Shares which are designed for investors who meet certain
                      administrative criteria and a minimum initial investment
                      of $10 million.
 
                      The shares of each Portfolio are fully paid and
                      non-assessable; have no preference as to conversion,
                      exchange, dividends, retirement or other features; and
                      have no pre-emptive rights. Such shares have
                      non-cumulative voting rights, meaning that the holders of
                      more than 50% of the shares voting for the election of
                      Directors can elect 100% of the Directors if they so
                      choose.
 
                                       20
<PAGE>   60
 
                      Annual meetings of shareholders will not be held except as
                      required by the Investment Company Act of 1940 and other
                      applicable law. An annual meeting will be held to vote on
                      the removal of a Director or Directors of the Fund if
                      requested in writing by the holders of not less than 10%
                      of the outstanding shares of the Fund.
 
                      All securities and cash for the Total Bond Market
                      Portfolio are held by Chase Manhattan Bank, New York, NY.
                      All securities and cash for the Short-Term Bond,
                      Intermediate-Term Bond and Long-Term Bond Portfolios are
                      held by State Street Bank and Trust Company, Boston, MA.
                      CoreStates Bank, N.A., Philadelphia, PA, holds daily cash
                      balances that are used by the Fund's Portfolios to invest
                      in repurchase agreements or securities acquired in these
                      transactions. The Vanguard Group, Inc., Valley Forge, PA,
                      serves as the Fund's Transfer and Dividend Disbursing
                      Agent. Price Waterhouse LLP, serves as independent
                      accountants for the Fund and will audit its financial
                      statements annually. The Fund is not involved in any
                      litigation.
- --------------------------------------------------------------------------------
 
                                       21
<PAGE>   61
 
                                 SERVICE GUIDE
 
PARTICIPATING IN
YOUR PLAN             The Portfolios are available as an investment option in
                      your retirement or savings plan. The administrator of your
                      plan or your employee benefits office can provide you with
                      detailed information on how to participate in your plan
                      and how to elect the Fund as an investment option.
 
                      If you have any questions about the Fund, including the
                      Portfolios' investment objectives, policies, risk
                      characteristics or historical performance, please contact
                      Participant Services (1-800-523-1188).
 
                      If you have questions about your account, contact your
                      plan administrator or the organization which provides
                      recordkeeping services for your plan.
- --------------------------------------------------------------------------------
INVESTMENT OPTIONS
ALLOCATIONS, AND
PAYROLL CHANGES       You may be permitted to elect different investment
                      options, alter the amounts contributed to your plan, or
                      change how contributions are allocated among your
                      investment options in accordance with your plan's specific
                      provisions. See your plan administrator or employee
                      benefits office for more details.
- --------------------------------------------------------------------------------
TRANSACTIONS IN
FUND SHARES           Purchases, exchanges or redemptions of a Portfolio's
                      shares are effective when received in "good order" by
                      Vanguard. "Good Order" means that complete information on
                      the purchase, exchange or redemption and the appropriate
                      signatures and monies have been received by Vanguard.
 
                      Vanguard must consider the interests of all Portfolio
                      shareholders. Therefore, for institutional investors who
                      are not participants in a retirement or savings plan, we
                      reserve the right to:
 
                      - Delay or reject any purchase or exchange request that
                        may disrupt a Portfolio's operation or performance.
 
                      - Revise or terminate the exchange privilege or limit the
                        amount of an exchange, at any time, without notice.
 
                      - Take up to seven days to deliver your redemption
                        proceeds.
 
                      - Pay redemption proceeds -- in whole or in
                        part -- through a distribution in kind of readily
                        marketable securities.
- --------------------------------------------------------------------------------
MAKING EXCHANGES      The exchange privilege (your ability to redeem shares from
                      one fund to purchase shares of another fund) may be
                      available to you through your plan. Although we make every
                      effort to maintain the exchange privilege, Vanguard
                      reserves the right to revise or terminate the exchange
                      privilege, limit the amount of an exchange, or reject any
                      exchange, at any time, without notice. Because excessive
                      exchanges can potentially disrupt the management of a Fund
                      and increase its transaction costs, Vanguard limits
                      exchange activity to TWO SUBSTANTIVE EXCHANGE REDEMPTIONS
                      (at least 30 days apart) from any Fund during any 12-month
                      period. "Substantive" means either a dollar amount or a
                      series of movements between Vanguard funds that Vanguard
                      determines, in its sole discretion, could have an adverse
                      impact on the management of the Fund. In addition, certain
                      investment options, particularly
 
                                       22
<PAGE>   62
 
                      funds made up of company stock or investment contracts,
                      may be subject to unique restrictions. Contact your plan
                      administrator for details on the exchange policies that
                      apply to your plan.
 
                      Before making an exchange, you should consider the
                      following:
 
                      - If you are making an exchange to another Vanguard Fund
                        option, please read the Fund's prospectus. Contact
                        Participant Services (1-800-523-1188) for a copy.
 
                      - Exchanges are accepted by Vanguard only as permitted by
                        your plan. Your plan administrator can explain how
                        frequently exchanges are allowed.
- --------------------------------------------------------------------------------
 
                                       23
<PAGE>   63
 
                      [THIS PAGE INTENTIONALLY LEFT BLANK]
<PAGE>   64
 
- --------------------------------------------------------------------------------
<TABLE>
<S>       <C>                         
          Vanguard Logo
          ---------------------------
          THE VANGUARD GROUP
          P.O. Box 2900
          Valley Forge, PA 19482
          INSTITUTIONAL PARTICIPANT
          SERVICES DEPARTMENT:
          1-800-523-1188
          TRANSFER AGENT:
          The Vanguard Group, Inc.
          P.O. Box 2900
          Valley Forge, PA 19482
          I084
 
<CAPTION>
<S>        <C>
                                  [Flag Logo]
                                BOND INDEX FUND
                      I  N  S  T  I  T  U  T  I  O  N  A  L
                          P  R  O  S  P  E  C  T  U  S
                                 APRIL 17, 1998
</TABLE>
1084
                         A MEMBER OF THE VANGUARD GROUP
- --------------------------------------------------------------------------------
<PAGE>   65
 
- --------------------------------------------------------------------------------
 
<TABLE>
<S>                             <C>                                   <C>
                                                                                                  LOGO
                                                                                                  LOGO
                                                                                 P   R   O   S   P   E   C   T   U   S
                                                                                             APRIL 17, 1998
                                                                                                  LOGO
</TABLE>
 
- --------------------------------------------------------------------------------
<PAGE>   66
 
- --------------------------------------------------------------------------------
 
================================================================================
LOGO
                                                  A Member of The Vanguard Group
================================================================================
 
PROSPECTUS -- APRIL 17, 1998
- --------------------------------------------------------------------------------
 
FUND INFORMATION: PARTICIPANT SERVICES -- 1-800-523-8066
- --------------------------------------------------------------------------------
 
INVESTMENT
OBJECTIVE
AND POLICIES          The Total Bond Market Portfolio of Vanguard Bond Index
                      Fund, Inc. (the "Portfolio"), is an open-end, diversified
                      investment company designed as an "index fund." The
                      objective of the Portfolio is to duplicate the total
                      return (income plus capital change) of publicly-traded
                      investment grade fixed-income securities in the aggregate
                      by attempting to duplicate the investment performance of a
                      certain investment grade bond index. The Portfolio invests
                      in a diversified portfolio of U.S. Government and
                      corporate bonds and mortgage-backed securities. There is
                      no assurance that the Portfolio will achieve its stated
                      objective. Shares of the Portfolio are neither insured nor
                      guaranteed by any agency of the U.S. Government, including
                      the FDIC.
- --------------------------------------------------------------------------------
 
INVESTMENT
ALTERNATIVES          The Total Bond Market Portfolio of Vanguard Bond Index
                      Fund, Inc. offers two separate classes of shares to
                      investors. The "Total Bond Market Portfolio Institutional
                      Shares" are designed primarily for investors who meet
                      certain administrative requirements and a minimum initial
                      investment of $10 million. Only the Institutional class of
                      shares is offered through this prospectus. The second
                      class of shares, "Total Bond Market Portfolio," is
                      available to all institutional and individual investors
                      and is offered through a separate prospectus. To obtain
                      information on the "Total Bond Market Portfolio" class of
                      shares, please call 1-800-662-7447 (SHIP), Monday through
                      Friday, from 8:00 a.m. to 9:00 p.m. and Saturday from 9
                      a.m. to 4:00 p.m. (Eastern time).
- --------------------------------------------------------------------------------
 
OPENING AN
ACCOUNT               Shares of the Portfolio may be purchased by Federal Funds
                      wire. The minimum initial investment is $10 million.
- --------------------------------------------------------------------------------
 
ABOUT THIS
PROSPECTUS            This Prospectus is designed to set forth concisely the
                      information you should know about the Portfolio before you
                      invest. It should be retained for future reference. A
                      "Statement of Additional Information" containing
                      additional information about the Fund has been filed with
                      the Securities and Exchange Commission. This Statement is
                      dated April 17, 1998 and has been incorporated by
                      reference into this Prospectus. A copy may be obtained
                      without charge by writing to the Fund, calling Participant
                      Services at 1-800-523-8066 or visiting the Securities and
                      Exchange Commission's website (www.sec.gov).
- --------------------------------------------------------------------------------
 
TABLE OF CONTENTS
 
<TABLE>
<CAPTION>
                Page                                       Page                                       Page
<S>                                        <C>                                        <C>
Portfolio Expenses................  2      Investment Risks ..................7       Performance Record ............... 14
Financial                                  Who Should Invest ................  9      Dividends, Capital Gains and
Highlights   ...............  3            Implementation of                          Taxes .... 14
Yield and Total                            Policies ..........  9                     The Share Price of The
Return   .............  4                  Investment                                 Portfolio ..... 16
                                           Limitations ............ 12                General
          FUND INFORMATION                 Management of the                          Information ............... 16
Investment                                 Portfolio ........ 12                      Shareholder Guide ................ 18
Objective   ..............  5              Investment
Investment                                 Adviser ................ 13
Policies   ................  5
</TABLE>
 
- --------------------------------------------------------------------------------
 
THESE SECURITIES HAVE NOT BEEN APPROVED OR DISAPPROVED BY THE SECURITIES AND
EXCHANGE COMMISSION, NOR HAS THE SECURITIES AND EXCHANGE COMMISSION PASSED UPON
THE ACCURACY OR ADEQUACY OF THIS PROSPECTUS. ANY REPRESENTATION TO THE CONTRARY
IS A CRIMINAL OFFENSE.
- --------------------------------------------------------------------------------
 
- --------------------------------------------------------------------------------
<PAGE>   67
 
PORTFOLIO
EXPENSES              The following tables illustrate ALL expenses and fees that
                      you would incur as a shareholder of the Total Bond Market
                      Portfolio Institutional shares and Total Bond Market
                      Portfolio. The expenses and fees set forth in the table
                      are for the 1997 fiscal year.
 
<TABLE>
<CAPTION>
                                                                               TOTAL BOND MARKET
                                                                                   PORTFOLIO         TOTAL BOND MARKET
                                     SHAREHOLDER TRANSACTION EXPENSES         INSTITUTIONAL SHARES       PORTFOLIO
                               <S>                                            <C>                    <C>
                               ---------------------------------------------------------------------------------------
                               Sales Load Imposed on Purchases*.............      None                  None
                               Sales Load Imposed on Reinvested Dividends...      None                  None
                               Redemption Fees**............................      None                  None
                               Exchange Fees................................      None                  None
</TABLE>
 
                       * The Portfolio reserves the right to deduct a portfolio
                         transaction fee of 0.18%, payable directly to the
                         Portfolio, from purchases of a size that is reasonably
                         deemed to be disruptive to efficient portfolio
                         management. See text below.
                      ** Wire redemptions of less than $5,000 are subject to a
                      $5 processing fee.
 
<TABLE>
<CAPTION>
                                      ANNUAL FUND OPERATING EXPENSES
                               <S>                                            <C>                    <C>
                               ---------------------------------------------------------------------------------------
                               Management & Administrative Expenses.........     0.05%                 0.14%
                               Investment Advisory Fees.....................      0.01                  0.01
                               12b-1 Fees...................................      None                  None
                               Other Expenses
                                   Distribution Costs.......................      0.03                  0.03
                                   Miscellaneous Expenses...................      0.01                  0.02
                                                                              ------------           -----------
                               Total Other Expenses.........................      0.04                  0.05
                                                                              ------------           -----------
                                        TOTAL OPERATING EXPENSES............     0.10%                 0.20%
                                                                              ==============         =============
</TABLE>
 
   
                      The purpose of these tables is to assist you in
                      understanding the various costs and expenses that you
                      would bear directly or indirectly as an investor in the
                      Portfolio.
    
 
TRANSACTION FEE       The Portfolio reserves the right to deduct a portfolio
                      transaction fee from purchases of the shares of the
                      Portfolio. Fees will not be charged on any investment
                      where the aggregate balance is expected to be less than
                      $50 million. Fees may be charged on the entire lump-sum
                      purchase for transactions that exceed or are expected to
                      exceed $50 million over the next twelve months if such
                      purchases are reasonably deemed to be disruptive to
                      efficient portfolio management. Lump-sum purchases over
                      $50 million may be considered disruptive, for example, if
                      the portfolio manager incurs significant transaction costs
                      in purchasing portfolio securities needed to match the
                      investment performance of the benchmark index. If such
                      purchases can be offset by redemptions of shares by other
                      shareholders, such fee may be waived or reduced. A
                      prospective investor may determine whether a fee will be
                      charged by calling his/her Institutional Investor Service
                      Representative in advance of his/her purchase. The fee, if
                      imposed, will be 0.18% of the purchase. The fee is based
                      on the portfolio manager's estimate of transaction costs,
                      which depends on the types of securities in which the
                      Portfolio invests.
 
                      The following example illustrates the expenses that you
                      would incur on a $1,000 investment over various periods,
                      assuming (1) a 5% annual rate of return and
 
                                        2
<PAGE>   68
 
                      (2) redemption at the end of each period. As noted in the
                      table on page 2, the Portfolio charges no redemption fees
                      of any kind.
 
<TABLE>
<CAPTION>
                                                                           1 YEAR   3 YEARS   5 YEARS   10 YEARS
                                                                           ------   -------   -------   --------
                               <S>                                         <C>      <C>       <C>       <C>
                               Total Bond Market
                                 Portfolio -- Institutional Shares.......   $ 1       $ 3       $ 6       $13
                               Total Bond Market Portfolio...............   $ 2       $ 6       $11       $26
</TABLE>
 
                      THIS EXAMPLE SHOULD NOT BE CONSIDERED A REPRESENTATION OF
                      PAST OR FUTURE EXPENSES OR PERFORMANCE. ACTUAL EXPENSES
                      MAY BE HIGHER OR LOWER THAN THOSE SHOWN.
- --------------------------------------------------------------------------------
 
FINANCIAL
HIGHLIGHTS            The following financial highlights for a share outstanding
                      throughout each period presented have been derived from
                      financial statements which were audited by Price
                      Waterhouse LLP, independent accountants, whose report
                      thereon was unqualified. This information should be read
                      in conjunction with the financial statements appearing in
                      the Fund's 1997 financial statements and notes thereto,
                      which, together with the remaining portions of the Fund's
                      1997 Annual Report to Shareholders, are incorporated by
                      reference in the Statement of Additional Information and
                      this Prospectus, and which appear, along with the report
                      of Price Waterhouse LLP, in the Fund's 1997 Annual Report
                      to Shareholders. For a more complete discussion of the
                      Fund's performance, please see the Fund's 1997 Annual
                      Report, which may be obtained without charge by writing to
                      the Fund or by calling our Investor Information Department
                      at 1-800-662-7447.
                             ---------------------------------------------------
                              TOTAL BOND MARKET PORTFOLIO -- INSTITUTIONAL CLASS
                             ---------------------------------------------------
 
   
<TABLE>
<CAPTION>
                                                                                           YEAR ENDED
                                                                                          DECEMBER 31,     SEPT. 18, 1995+ TO
                                                                                          1997     1996      DEC. 31, 1995
                               ----------------------------------------------------------------------------------------------
                               <S>                                                       <C>      <C>      <C>
                               NET ASSET VALUE, BEGINNING OF YEAR......................  $ 9.84   $10.14         $ 9.87
                                                                                         ------   ------   ------------
                               INVESTMENT OPERATIONS
                                 Net Investment Income.................................    .655     .650           .174
                                 Net Realized and Unrealized Gain (Loss) on
                                   Investments.........................................    .250    (.300)          .270
                                                                                         ------   ------   ------------
                                       TOTAL FROM INVESTMENT OPERATIONS................    .905     .350           .444
                               ----------------------------------------------------------------------------------------------
                               DISTRIBUTIONS
                                 Dividends from Net Investment Income..................   (.655)   (.650)         (.174)
                                 Dividends from Realized Capital Gains.................      --       --             --
                                                                                         ------   ------   ------------
                                       TOTAL DISTRIBUTIONS.............................   (.655)   (.650)         (.174)
                               ----------------------------------------------------------------------------------------------
                               NET ASSET VALUE, END OF YEAR............................  $10.09   $ 9.84         $10.14
                               ==============================================================================================
                               TOTAL RETURN............................................    9.55%    3.68%          4.53%
                               ==============================================================================================
                               RATIOS/SUPPLEMENTAL DATA
                               Net Assets, End of Year (Millions)......................  $1,628   $1,024            $413
                               Ratio of Total Expenses to Average Net Assets...........    0.10%    0.10%          0.10%*
                               Ratio of Net Investment Income to Average Net Assets....    6.64%    6.66%          6.48%*
                               Portfolio Turnover Rate.................................      39%      39%            36%
                               * Annualized.
                               + Commencement of operations.
</TABLE>
    
 
                                        3
<PAGE>   69
 
   
<TABLE>
<CAPTION>
                                      -------------------------------------------------------------------------------------------
                                                                      TOTAL BOND MARKET PORTFOLIO
                                      -------------------------------------------------------------------------------------------
                                                                        YEAR ENDED DECEMBER 31,
                                      -------------------------------------------------------------------------------------------
                                       1997     1996     1995     1994     1993     1992     1991     1990     1989     1988
- ---------------------------------------------------------------------------------------------------------------------------------
<S>                                   <C>      <C>      <C>      <C>      <C>      <C>      <C>      <C>      <C>      <C>    <C>
NET ASSET VALUE, BEGINNING OF
  YEAR..............................  $ 9.84   $10.14   $ 9.17   $10.06   $ 9.88   $ 9.99   $ 9.41   $ 9.44   $ 9.05   $ 9.20
                                      ------   ------   ------   ------   ------   ------   ------   ------   ------   ------
INVESTMENT OPERATIONS
  Net Investment Income.............    .645     .640     .650     .622     .638     .699     .766     .796     .797     .807
  Net Realized and Unrealized
    Gain (Loss) on Investments......    .250    (.300)    .970    (.888)    .300    (.018)    .605    (.030)    .390    (.150)
                                      ------   ------   ------   ------   ------   ------   ------   ------   ------   ------
      TOTAL FROM INVESTMENT
        OPERATIONS..................    .895     .340    1.620    (.266)    .938     .681    1.371     .766    1.187     .657
- ---------------------------------------------------------------------------------------------------------------------------------
DISTRIBUTIONS
  Dividends from Net Investment
    Income..........................   (.645)   (.640)   (.650)   (.622)   (.638)   (.699)   (.766)   (.796)   (.797)   (.807)
  Distributions from Realized
    Capital Gains...................      --       --    (.002)   (.120)   (.092)   (.025)      --       --       --       --
                                      ------   ------   ------   ------   ------   ------   ------   ------   ------   ------
      TOTAL DISTRIBUTIONS...........   (.645)   (.640)   (.650)   (.624)   (.758)   (.791)   (.791)   (.796)   (.797)   (.807)
- ---------------------------------------------------------------------------------------------------------------------------------
NET ASSET VALUE, END OF YEAR........  $10.09   $ 9.84   $10.14   $ 9.17   $10.06   $ 9.88   $ 9.99   $ 9.41   $ 9.44   $ 9.05
=================================================================================================================================
TOTAL RETURN (1)....................    9.44%    3.58%   18.18%   (2.66)%   9.68%    7.14%   15.25%    8.65%   13.65%    7.35%
=================================================================================================================================
RATIOS/SUPPLEMENTAL DATA
Net Assets, End of Year
  (Millions)........................  $5,129   $2,962   $2,405   $1,731   $1,540   $1,066     $849     $277     $139      $58
Ratio of Total Expenses to Average
  Net Assets........................    0.20%    0.20%    0.20%    0.18%    0.18%    0.20%    0.16%    0.21%    0.24%    0.30%
Ratio of Net Investment Income to
  Average Net Assets................    6.54%    6.54%    6.66%    6.57%    6.24%    7.06%    7.95%    8.60%    8.49%    8.84%
Portfolio Turnover Rate.............      39%      39%      36%      33%      50%      49%      31%      29%      33%      21%
(1) Total return figures do not reflect the annual account maintenance fee of $10 (charged to individual investors).
</TABLE>
    
 
- --------------------------------------------------------------------------------
 
YIELD AND
TOTAL RETURN          From time to time the Portfolio may advertise its yield
                      and total return. Both yield and total return figures are
                      based on historical earnings and are not intended to
                      indicate future performance. The "total return" of a
                      Portfolio refers to the average annual compounded rates of
                      return over one-, five- and ten-year periods or for the
                      life of the Portfolio (as stated in the advertisement)
                      that would equate an initial amount invested at the
                      beginning of a stated period to the ending redeemable
                      value of the investment, assuming the reinvestment of all
                      dividend and capital gains distributions.
 
                      In accordance with industry guidelines set forth by the
                      U.S. Securities and Exchange Commission, the "30-day
                      yield" of a Portfolio is calculated by dividing the net
                      investment income per share earned during a 30-day period
                      by the net asset value per share on the last day of the
                      period. Net investment income includes interest and
                      dividend income earned on the Portfolio's securities; it
                      is net of all expenses and all recurring and nonrecurring
                      charges that have been applied to all shareholder
                      accounts. The yield calculation assumes that the net
                      investment income earned over 30 days is compounded
                      monthly for six months and then annualized. Methods used
                      to calculate advertised yields are standardized for all
                      stock and bond mutual funds. However, these methods differ
                      from the accounting methods used by the Portfolio to
                      maintain its books and records, and so the advertised
                      30-day yield may not fully reflect the income paid to an
                      investor's account.
- --------------------------------------------------------------------------------
 
                                        4
<PAGE>   70
 
INVESTMENT
OBJECTIVE             The Institutional Shares are designed primarily for
                      institutional investors. The Total Bond Market Portfolio
                      is a no-load, open-end diversified investment company
                      designed as an "index" fund. The Portfolio invests in
                      fixed-income securities with prescribed maturity and
                      credit quality standards in order to match the investment
                      performance of the Lehman Brothers Aggregate Bond Index
                      (the "Index"). The Index is a broad market-weighted index
                      which encompasses U.S. Treasury and agency securities,
                      corporate investment grade bonds, international
                      (dollar-denominated) investment grade bonds, and
                      mortgage-backed securities. There is no assurance that the
                      Portfolio will achieve its stated objective.
 
                      The investment objective of the Portfolio is fundamental
                      and so cannot be changed without the approval of a
                      majority of the Portfolio's shareholders.
- --------------------------------------------------------------------------------
 
INVESTMENT
POLICIES
THE PORTFOLIO USES A
"PASSIVE" APPROACH
TO INVEST IN FIXED-
INCOME SECURITIES     The Portfolio is not managed according to traditional
                      methods of "active" investment management, which involve
                      the buying and selling of securities based upon economic,
                      financial, and market analyses and investment judgment.
                      Instead, the Portfolio, utilizing a "passive" or
                      "indexing" investment approach, will attempt to duplicate
                      the investment performance of its benchmark index through
                      statistical sampling procedures. The Portfolio will invest
                      in a group of fixed-income securities selected from the
                      Index which, when taken together, are expected to perform
                      similarly to the Index as a whole. This sampling technique
                      is expected to enable the Portfolio to track the dividend
                      income and price movements of the Index, while minimizing
                      brokerage, custodial and accounting costs. The Portfolio
                      is managed without regard to tax ramifications.
 
                      The TOTAL BOND MARKET PORTFOLIO will invest in a portfolio
                      of fixed-income securities selected to match the Lehman
                      Brothers Aggregate Bond Index. The Index is a broad
                      market-weighted index which encompasses four major classes
                      of investment grade fixed-income securities in the United
                      States: U.S. Treasury and agency securities, corporate
                      bonds, international (dollar-denominated) bonds, and
                      mortgage-backed securities, with maturities greater than
                      one year.
 
                      The Portfolio will invest 80% or more of its assets in
                      securities included in the Index. As of December 31, 1997,
                      the major classes of fixed-income securities represented
                      the following proportions of the Index's total market
                      value:
 
<TABLE>
<CAPTION>
                                                                                          LEHMAN
                                                                                        AGGREGATE
                                                                                        BOND INDEX
                                                                                        ----------
                               <S>                                                      <C>
                               U.S. Treasury and agency securities                           49%
                               Corporate bonds                                               17%
                               International (dollar-denominated) bonds                       4%
                               Mortgage-backed securities                                    30%
                               Dollar-weighted average maturity (Years)                  8.7 yrs
</TABLE>
 
                                        5
<PAGE>   71
 
                      The Portfolio may, from time to time, substitute one type
                      of investment grade bond for another. For instance, the
                      Portfolio may hold more short-term corporate bonds (fewer
                      short-term U.S. Treasury bonds) than represented in the
                      Index so as to increase income. This corporate
                      substitution strategy will entail the assumption of
                      additional credit risk; however, substantial
                      diversification within the corporate sector should
                      moderate issue-specific credit risk. In addition, current
                      investment policy restricts corporate substitutions to
                      issues with less than 4 years remaining to maturity and in
                      aggregate no more than 15% of net assets. Overall, credit
                      risk is expected to be very low.
 
                      Fixed-income securities will be primarily of investment
                      grade quality -- i.e., those rated at least Baa3 by
                      Moody's Investors Service, Inc. or BBB- by Standard &
                      Poor's Corporation. Securities rated Baa or BBB are
                      considered as medium grade obligations. Interest payments
                      and principal are regarded as adequate for the present but
                      certain protective elements found in higher rated bonds
                      may be lacking. Such bonds lack outstanding investment
                      characteristics and, in fact, have speculative
                      characteristics as well.
 
                      In its effort to duplicate the investment performance of
                      the Index, the Portfolio will invest in fixed-income
                      securities approximating its relative proportion of the
                      Index's total market value. For the Total Bond Market
                      Portfolio, these investments will include U.S. Treasury
                      and agency securities, mortgage-backed securities and
                      corporate and international (dollar-denominated) bonds.
                      The Portfolio may invest in U.S. Treasury bills, notes and
                      bonds and other "full faith and credit" obligations of the
                      U.S. Government. The Portfolio may also invest in U.S.
                      Government agency securities, which are debt obligations
                      issued or guaranteed by agencies or instrumentalities of
                      the U.S. Government. Such "agency" securities may not be
                      backed by the "full faith and credit" of the U.S.
                      Government. Such U.S. Government agencies may include the
                      Federal Farm Credit Banks, the Resolution Trust
                      Corporation and the Government National Mortgage
                      Association. Even though they all carry top (AAA) credit
                      ratings, "agency" obligations are not explicitly
                      guaranteed by the U.S. Government and so are perceived as
                      somewhat riskier than comparable Treasury bonds.
 
                      The Portfolio may also invest up to 20% of its assets in
                      short-term money market instruments, and may invest in
                      bond (interest rate) futures contracts and options to a
                      limited extent. Such securities will be held only to
                      invest uncommitted cash balances, to maintain liquidity to
                      meet shareholder redemptions, or to minimize trading
                      costs. The Portfolio will not invest in such securities as
                      part of a temporary defensive strategy (such as altering
                      the aggregate maturity of the Portfolio) to protect the
                      Fund against potential bond market declines. The Portfolio
                      intends to remain fully invested, to the extent
                      practicable, in a pool of securities which will duplicate
                      the investment characteristics of the benchmark index. See
                      "Implementation of Policies" for a description of other
                      investment practices of the Portfolio.
 
                                        6
<PAGE>   72
 
                      The Portfolio is responsible for voting the shares of all
                      securities it holds.
 
                      These investment policies are not fundamental and so may
                      be changed by the Board of Directors without shareholder
                      approval. However, shareholders would be notified prior to
                      any material change in investment policies.
- --------------------------------------------------------------------------------
 
INVESTMENT
RISKS                 As a mutual fund investing primarily in fixed-income
                      securities, the Portfolio is subject to interest rate,
                      income, call and credit risks. Since the Total Bond Market
                      Portfolio also invests in mortgage-backed securities, the
                      Portfolio is also subject to prepayment risk.
 
THE PORTFOLIO IS
SUBJECT TO INTEREST
RATE RISK             INTEREST RATE RISK is the potential for fluctuations in
                      bond prices due to changing interest rates. As a rule,
                      bond prices vary inversely with interest rates. If
                      interest rates rise, bond prices generally decline; if
                      interest rates fall, bond prices generally rise. In
                      addition, for a given change in interest rates,
                      longer-maturity bonds fluctuate more in price than
                      shorter-maturity bonds. To compensate investors for these
                      larger fluctuations, longer-maturity bonds usually offer
                      higher yields than shorter-maturity bonds, other factors,
                      including credit quality, being equal.
 
                      These basic principles of bond prices also apply to U.S.
                      Government securities. A security backed by the "full
                      faith and credit" of the U.S. Government is guaranteed
                      only as to its stated interest rate and face value at
                      maturity, not its current market price. Just like other
                      fixed-income securities, government-guaranteed securities
                      will fluctuate in value when interest rates change.
 
                      The TOTAL BOND MARKET PORTFOLIO maintains an
                      intermediate-term dollar-weighted average maturity, and is
                      therefore subject to a moderate to high level of interest
                      rate risk. As an illustration of interest rate risk, the
                      chart below depicts the effect of a two percentage point
                      change in interest rates on three bonds of varying
                      maturities:
 
                        PERCENTAGE CHANGE IN PRICE OF A PAR BOND YIELDING 7.5%
 
                      ----------------------------------------------------------
 
<TABLE>
<CAPTION>
                                                                    2 PERCENTAGE POINT   2 PERCENTAGE POINT
                                                                       INCREASE IN          DECREASE IN
                                         STATED MATURITY              INTEREST RATES       INTEREST RATES
                               -------------------------------      ------------------   ------------------
                               <S>                                  <C>                  <C>
                               Short-Term (2.5 years)                     - 4.4%               + 4.6%
                               Intermediate-Term (10 years)               -12.7%               +15.2%
                               Long-Term (20 years)                       -17.8%               +24.1%
</TABLE>
 
                      This chart is intended to provide you with guidelines for
                      determining the degree of interest rate risk you may be
                      willing to assume. The yield and price changes shown
                      should not be taken as representative of the Portfolio's
                      current or future yield or expected changes in the
                      Portfolio's share price.
 
THE PORTFOLIO IS
SUBJECT TO INCOME
RISK                  INCOME RISK is the potential for a decline in the
                      Portfolio's income due to falling market interest rates.
 
                                        7
<PAGE>   73
 
THE PORTFOLIO
IS SUBJECT TO
PREPAYMENT RISK       As a mutual fund investing a portion of its assets in
                      mortgage-backed securities (see chart on page 5), the
                      Total Bond Market Portfolio is subject to prepayment risk
                      to a limited extent. PREPAYMENT RISK is the possibility
                      that, during periods of declining interest rates, the
                      principal invested in high-yielding mortgage-backed
                      securities will be repaid earlier than scheduled, and the
                      Portfolio will be forced to reinvest the unanticipated
                      payments at generally lower interest rates.
 
                      Prepayment risk has two important effects on the
                      Portfolio. First, when interest rates fall and principal
                      prepayments are reinvested at lower interest rates, the
                      income that the Portfolio derives from mortgage-backed
                      securities is reduced. Second, like other fixed-income
                      securities, mortgage-backed securities generally decline
                      in price when interest rates rise. However, because of
                      prepayment risk, mortgage-backed securities (and thus in
                      part the share price of the Portfolio and the value of the
                      Index) will not enjoy as large a gain in market value as
                      ordinary bonds when interest rates fall. In part to
                      compensate for prepayment risk, mortgage-backed securities
                      generally offer higher yields than bonds of comparable
                      credit quality and maturity.
 
CREDIT RISK IS
EXPECTED TO BE LOW    CREDIT RISK is the possibility that an issuer of
                      securities held by the Portfolio will be unable to make
                      payments of either interest or principal. The credit risk
                      of the Portfolio is a function of the credit quality of
                      its underlying securities.
 
                      The credit quality of the Portfolio is expected to be very
                      high, and thus credit risk should be low. As of December
                      31, 1997, the average quality, as rated by Moody's
                      Investors Service, Inc., was Aaa for the Aggregate Bond
                      Index.
 
                      To a limited extent, the Portfolio is also exposed to
                      EVENT RISK, the possibility that corporate fixed-income
                      securities held by the Portfolio may suffer a substantial
                      decline in credit quality and market value due to a
                      corporate restructuring. Corporate restructurings, such as
                      mergers, leveraged buyouts, takeovers or similar events,
                      are often financed by a significant expansion of corporate
                      debt. As a result of the added debt burden, the credit
                      quality and market value of a firm's existing debt
                      securities may decline significantly. While event risk may
                      be high for certain corporate and international
                      (dollar-denominated) securities held by the Portfolio,
                      event risk for the Portfolio in the aggregate should be
                      low because of the Portfolio's diversified holdings and
                      the small percentage of the Portfolio's assets invested in
                      these securities.
 
                      The corporate substitution strategy will increase credit
                      risk somewhat, as short-term investment grade corporate
                      bonds are substituted for U.S. Treasury bonds and notes;
                      however, owing to the diversified nature of the Portfolio,
                      and policies limiting the maturity and maximum amount of
                      substitutions, the overall credit and event risk of the
                      Portfolio is expected to be low.
 
NO CURRENCY RISK
IN THE PORTFOLIO
                      While the Aggregate Bond Index does have limited exposure
                      to international bonds, there is no currency risk
                      associated with the investments since they are all
                      dollar-denominated.
- --------------------------------------------------------------------------------
 
                                        8
<PAGE>   74
 
WHO SHOULD
INVEST
INVESTORS SEEKING TO
PARTICIPATE IN THE
"BOND MARKET"
AS A WHOLE            The Portfolio is designed for individual and institutional
                      investors seeking well-diversified, low-cost ways to
                      participate in the U.S. fixed-income markets. The
                      Portfolio will be essentially fully invested at all times.
                      Because the Total Bond Market Portfolio will represent all
                      major sectors of the investment grade fixed-income
                      securities market, the Portfolio is a suitable vehicle for
                      those investors seeking ownership in the "bond market" as
                      a whole, without regard to particular sectors. The
                      Portfolio concentrates on bonds of various maturities.
                      Because of the risks associated with bond investments, the
                      Portfolio is intended to be a long-term investment vehicle
                      and is not designed to provide investors with a means of
                      speculating on short-term bond market movements. Investors
                      seeking to temporarily (less than two years) gain broad
                      bond market exposure at a low cost can generate excessive
                      transaction costs resulting in a risk of poor index
                      tracking.
 
   
                      As with all longer-term, fixed-income investments, the
                      share price of the Total Bond Market Portfolio will vary.
                      Credit risk should be minimal for the Portfolio. The
                      investment risks are described on pages 7 and 8.
    
 
                      The Portfolio is also suitable for those investors with
                      existing common stock holdings who are seeking a
                      complementary fixed-income investment to create a more
                      balanced asset mix. Because of potential share price
                      fluctuations, the Portfolio may be inappropriate for
                      investors who have short-term objectives or who require
                      stability of principal.
- --------------------------------------------------------------------------------
 
IMPLEMENTATION
OF POLICIES           The Portfolio follows a variety of investment practices in
                      an effort to duplicate the total return of its benchmark
                      index.
 
THE PORTFOLIO INVESTS
IN FIXED INCOME
SECURITIES            The Portfolio will invest at least 80% or more of its
                      assets in securities included in its benchmark Index. The
                      Index measures the total investment return (capital change
                      plus income) provided by a universe of fixed-income
                      securities with maturities greater than one year, weighted
                      by the market value outstanding of each security. The
                      securities included in the Index generally meet the
                      following criteria, as defined by Lehman Brothers: an
                      outstanding market value of at least $100 million; and
                      investment grade quality -- i.e., rated a minimum of Baa3
                      by Moody's Investors Service, Inc. If a security held in
                      the Fund's portfolio is downgraded to a rating below these
                      minimum standards, the Fund may continue to hold it until
                      such time as the adviser deems it most advantageous to
                      dispose of the security.
 
THE PORTFOLIO USES A
"SAMPLING" TECHNIQUE  The Portfolio will be unable to hold all of the individual
                      issues which comprise the Index because of the large
                      number of securities involved. Instead, the Portfolio will
                      hold a representative sample of the securities in its
                      benchmark index, selecting a few issues to represent
                      entire "classes" or types of securities in the Index. The
                      Portfolio will be constructed so as to approximately match
                      the composition of its benchmark index as described on
                      page 5 after adjusting for the corporate substitution
                      policy described on page 6.
 
                      At the broadest level, and adjusted for the corporate
                      substitution strategy, the Portfolio will seek to hold
                      securities which reflect the weighting of the major asset
                      classes in its benchmark index. These classes include U.S.
                      Treasury and agency
 
                                        9
<PAGE>   75
 
                      securities, corporate bonds, and mortgage-backed
                      securities. If U.S. Treasury and agency securities
                      represent approximately 60% of the Index's interest rate
                      risk, then approximately 60% of the Portfolio's interest
                      rate risk will come from such securities. Similarly, if
                      corporate bonds represent 20% of the interest rate risk of
                      the Index, then they will represent approximately 20% of
                      the interest rate risk of the Portfolio.
 
                      Such a sampling technique is expected to be an effective
                      means of substantially duplicating the income and capital
                      returns provided by the Index. Over time, the correlation
                      between the performance of the Portfolio and the Index is
                      expected to be 0.95 or higher. A correlation of 1.00 would
                      indicate perfect correlation, which would be achieved when
                      the net asset value of the Portfolio, including the value
                      of its dividend and capital gains distributions, increases
                      or decreases in exact proportion to changes in the Index.
                      The performance and structure of the Portfolio versus that
                      of the Index is monitored regularly. If significant
                      structural mismatches develop, the Portfolio is rebalanced
                      to bring it in line with the Index.
 
THE PORTFOLIO
MAY INVEST IN
MORTGAGE-BACKED
SECURITIES            As part of its effort to duplicate the investment
                      performance of its Index, the Portfolio may invest in
                      mortgage-backed securities. Mortgage-backed securities
                      represent an interest in an underlying pool of mortgages.
                      Unlike ordinary fixed-income securities, which generally
                      pay a fixed rate of interest and return principal upon
                      maturity, mortgage-backed securities repay both interest
                      income and principal as part of their periodic payments.
                      Because the mortgages underlying mortgage-backed
                      certificates can be prepaid at any time by homeowners or
                      corporate borrowers, mortgage-backed securities give rise
                      to certain unique "prepayment" risks. See "Investment
                      Risks."
 
                      The Total Bond Market Portfolio may purchase
                      mortgage-backed securities issued by the Government
                      National Mortgage Association (GNMA), the Federal Home
                      Loan Mortgage Corporation (FHLMC), the Federal National
                      Mortgage Association (FNMA), and the Federal Housing
                      Authority (FHA). GNMA securities are guaranteed by the
                      U.S. Government as to the timely payment of principal and
                      interest; securities from other Government-sponsored
                      entities are generally not secured by an explicit pledge
                      of the U.S. Government. The Portfolio may also invest in
                      conventional mortgage securities, which are packaged by
                      private corporations and are not guaranteed by the U.S.
                      Government. Mortgage securities that are guaranteed by the
                      U.S. Government are guaranteed only as to the timely
                      payment of principal and interest. The market value of
                      such securities is not guaranteed and may fluctuate.
 
THE PORTFOLIO MAY
INVEST IN SHORT-TERM
MONEY MARKET
INSTRUMENTS           Although the Portfolio normally seeks to remain
                      substantially fully invested in securities in the Index,
                      the Portfolio may invest temporarily in certain short-term
                      money market instruments. Such securities may be used to
                      invest uncommitted cash balances or to maintain liquidity
                      to meet shareholder redemptions. These securities include:
                      obligations of the United States Government and its
                      agencies or instrumentalities; commercial paper, bank
                      certificates of deposit, and bankers' acceptances; and
                      repurchase agreements collateralized by these securities.
 
                                       10
<PAGE>   76
 
THE PORTFOLIO MAY
LEND ITS SECURITIES   The Portfolio may lend its investment securities to
                      qualified institutional investors for either short-term or
                      long-term purposes of realizing additional income. Loans
                      of securities by a Portfolio will be collateralized by
                      cash, letters of credit, or securities issued or
                      guaranteed by the U.S. Government or its agencies. The
                      collateral will equal at least 100% of the current market
                      value of the loaned securities.
 
PORTFOLIO TURNOVER
IS NOT EXPECTED TO
EXCEED 50%            Although it generally seeks to invest for the long term,
                      the Portfolio retains the right to sell securities
                      irrespective of how long they have been held. It is
                      anticipated that the annual portfolio turnover of the
                      Portfolio will not exceed 50%. A turnover rate of 50%
                      would occur, for example, if one half of the securities of
                      the Portfolio were replaced within one year. A portfolio
                      turnover rate of 100% may be considered high for a bond
                      index fund and would result in additional expenses.
 
DERIVATIVE
INVESTING             Derivatives are instruments whose values are linked to or
                      derived from an underlying security or index. The most
                      common and conventional types of derivative securities are
                      futures and options.
 
THE PORTFOLIO MAY
INVEST IN DERIVATIVE
SECURITIES            The Portfolio may invest in futures contracts and options,
                      but only to a limited extent. Specifically, the Portfolio
                      may enter into futures contracts provided that not more
                      than 5% of its assets are required as a futures contract
                      deposit; in addition, the Portfolio may enter into futures
                      contracts and options transactions only to the extent that
                      obligations under such contracts or transactions represent
                      not more than 20% of the Portfolio's assets.
 
                      Futures contracts and options may be used for several
                      common fund management strategies: to maintain cash
                      reserves while simulating full investment, to facilitate
                      trading, to reduce transaction costs, or to seek higher
                      investment returns when a specific futures contract is
                      priced more attractively than other futures contracts or
                      the underlying security or index.
 
                      The Portfolio may use futures contracts for bona fide
                      "hedging" purposes. In executing a hedge, a manager sells,
                      for example, stock index futures to protect against a
                      decline in the stock market. As such, if the market drops,
                      the value of the futures position will rise, thereby
                      offsetting the decline in value of the Portfolio's stock
                      holdings.
 
                      The Portfolio may also invest in other conventional
                      derivatives designed to replicate the risk/return
                      characteristics of a conventional fixed income note or
                      bond. Such derivatives would be managed, in both structure
                      and concentration, to adhere to the Fund's investment
                      policy restrictions as to market and credit risk.
 
THE PORTFOLIO MAY
INVEST IN CMOS        The Portfolio may invest in a relatively conservative
                      class of collateralized mortgage obligations (CMOs) which
                      feature a high degree of cash flow predictability and less
                      vulnerability to mortgage prepayment risk. To reduce
                      credit risk, Vanguard purchases these less risky classes
                      of collateralized mortgage obligations issued only by
                      agencies of the U.S. Government or privately-issued
                      collateralized mortgage obligations that carry
                      high-quality investment-grade ratings.
 
FUTURES CONTRACTS
AND OPTIONS POSE
CERTAIN RISKS         The primary risks associated with the use of futures
                      contracts and options are: (i) imperfect correlation
                      between the change in market value of the bonds held by a
                      Portfolio and the prices of futures contracts and options,
                      and (ii) possible lack of the liquid secondary market for
                      a futures contract and the resulting inability to close a
 
                                       11
<PAGE>   77
 
                      futures position prior to its maturity date. The risk of
                      imperfect correlation will be minimized by investing in
                      those contracts whose price fluctuations are expected to
                      resemble those of the Portfolio's underlying securities.
                      The risk that the Portfolio will be unable to close out a
                      futures position will be minimized by entering into such
                      transactions on a national exchange with an active and
                      liquid secondary market.
 
                      The risk of loss in trading futures contracts in some
                      strategies can be substantial, due both to the low margin
                      deposits required and the extremely high degree of
                      leverage involved in futures pricing. As a result, a
                      relatively small price movement in a futures contract may
                      result in immediate and substantial loss (or gain) to the
                      investor. When investing in futures contracts, the
                      Portfolio will segregate cash or other liquid portfolio
                      securities in the amount of the underlying obligation.
- --------------------------------------------------------------------------------
 
INVESTMENT
LIMITATIONS
THE PORTFOLIO HAS
ADOPTED CERTAIN
FUNDAMENTAL
LIMITATIONS           The Portfolio has adopted limitations on some of its
                      investment policies. Some of those limitations are that
                      the Portfolio will not:
 
                      (a) invest more than 5% of its assets in the securities of
                          any single issuer except obligations of the United
                          States Government or government agencies;
                      (b) purchase more than 5% of the voting securities of any
                          issuer;
                      (c) borrow money, except from banks for temporary or
                          emergency (not leveraging) purposes, including the
                          meeting of redemption requests which might otherwise
                          require the untimely disposition of securities, in an
                          amount not exceeding of 15% of the value of the
                          Portfolio's net assets (including the amount borrowed
                          and the value of any outstanding reverse repurchase
                          agreements) at the time the borrowing is made.
                          Whenever borrowings exceed 5% of the value of the
                          Portfolio's net assets, the Portfolio will not make
                          any additional investments;
                      (d) pledge, mortgage or hypothecate its assets to an
                          extent greater than 5% of the value of its total
                          assets; and
                      (e) invest more than 25% of its assets in any one
                          industry.
 
                      A complete list of the Portfolio's investment limitations
                      can be found in the Statement of Additional Information.
                      These limitations are fundamental and may be changed only
                      by approval of a majority of the Portfolio's shareholders.
- --------------------------------------------------------------------------------
 
   
MANAGEMENT
OF THE PORTFOLIO
VANGUARD ADMINISTERS
AND DISTRIBUTES THE
PORTFOLIO             The Portfolio is a member of The Vanguard Group of
                      Investment Companies, a family of more than 30 investment
                      companies with more than 95 distinct portfolios and total
                      assets in excess of $360 billion. Through their
                      jointly-owned subsidiary, The Vanguard Group, Inc.
                      ("Vanguard"), the Fund and the other funds in the Group
                      obtain at cost virtually all of their corporate
                      management, administrative, shareholder accounting and
                      distribution services. Vanguard also provides investment
                      advisory services on an at-cost basis to certain Vanguard
                      funds. As a result of Vanguard's unique corporate
                      structure, the Vanguard funds have costs substantially
                      lower than those of most competing mutual funds. In 1997,
                      the average expense ratio (annual costs including advisory
                      fees divided by total net assets) for the Vanguard funds
                      amounted to approximately .28% compared to an average of
                      1.24% for the mutual fund industry (data provided by
                      Lipper Analytical Services).
    
 
                                       12
<PAGE>   78
 
                      The Officers of the Fund manage its day-to-day operations
                      and are responsible to the Fund's Board of Directors. The
                      Directors set broad policies for the Fund and choose its
                      Officers. A list of the Directors and Officers of the Fund
                      and a statement of their present positions and principal
                      occupations during the past five years can be found in the
                      Statement of Additional Information.
 
                      Vanguard employs a supporting staff of management and
                      administrative personnel to provide the requisite services
                      to the funds and also furnishes the funds with necessary
                      office space, furnishings and equipment. Each fund pays
                      its share of Vanguard's net expenses, which are allocated
                      among the funds under methods approved by the Board of
                      Directors (Trustees) of each fund. In addition, each fund
                      bears its own direct expenses, such as legal, auditing and
                      custodian fees.
 
                      Vanguard also provides distribution and marketing services
                      to the Vanguard funds. The funds are available on a
                      no-load basis (i.e., there are no sales commissions or
                      12b-1 fees). However, each fund bears its share of the
                      Group's distribution costs.
- --------------------------------------------------------------------------------
 
   
INVESTMENT
ADVISER
VANGUARD MANAGES
THE FUND'S
INVESTMENTS           The Portfolio receives all investment advisory services
                      from Vanguard's Fixed Income Group. The Fixed Income Group
                      provides investment advisory services to more than 40
                      Vanguard money market and bond portfolios, both taxable
                      and tax-exempt. Total assets under management by
                      Vanguard's Fixed Income Group were more than $100 billion
                      as of December 31, 1997. The Portfolio is not actively
                      managed, but is instead administered by the Fixed Income
                      Group using computerized, quantitative techniques. The
                      Fixed Income Group is supervised by the Officers of the
                      Fund. Ian A. MacKinnon, Managing Director of Vanguard, has
                      been in charge of the Group since its inception in 1981.
    
 
                      Mr. MacKinnon is responsible for setting the broad
                      investment strategies employed by the Fund, and for
                      overseeing the portfolio manager who implements these
                      strategies on a day-to-day basis.
 
                      The Fund's portfolio manager is Kenneth E. Volpert, a
                      Principal of Vanguard, who also serves as portfolio
                      manager of the Vanguard Variable Insurance Fund -- High-
                      Grade Bond Portfolio and the bond portion of the Vanguard
                      Balanced Index Fund. Mr. Volpert began managing the
                      Vanguard Bond Index Fund in December, 1992. For six years
                      prior to joining Vanguard, Mr. Volpert was associated with
                      Mellon Bond Associates.
 
                      The Fixed Income Group places all orders for purchases and
                      sales of portfolio securities. Purchases of portfolio
                      securities are made either directly from the issuer or
                      from securities dealers. The Fixed Income Group may sell
                      portfolio securities prior to their maturity if
                      circumstances and considerations warrant and if it
                      believes such dispositions advisable. The Group seeks to
                      obtain the best available net price and most favorable
                      execution for all portfolio transactions. When the
                      Portfolio purchases a newly issued security at a fixed
                      price, the Group may designate certain members of the
                      underwriting syndicate to receive compensation associated
                      with that transaction. Certain dealers have agreed to
                      rebate a portion of such compensation directly to the
                      Portfolio to offset its management expenses.
- --------------------------------------------------------------------------------
 
                                       13
<PAGE>   79
 
PERFORMANCE
RECORD                The tables in this section provide investment results for
                      the Total Bond Market, Short-Term Bond, Intermediate-Term
                      Bond and Long-Term Bond Portfolios for several periods
                      throughout the Fund's lifetime. The results shown
                      represent "total return" investment performance, which
                      assumes the reinvestment of all capital gains and income
                      dividends for the indicated periods. Also included is
                      comparative information with respect to the unmanaged
                      Aggregate Bond Index described on page 5, the Consumer
                      Price Index, a statistical measure of changes in the
                      prices of goods and services, the Lehman Mutual Fund
                      Short-Term (1-5) Government/ Corporate Bond Index, the
                      Lehman Mutual Fund Intermediate (5-10) Government/
                      Corporate Bond Index, and the Lehman Long (10+)
                      Government/Corporate Bond Index.
 
                      The results shown should not be considered a
                      representation of the total return from an investment made
                      in the Portfolio today. This information is provided to
                      help investors better understand the Portfolio and may not
                      provide a basis for comparison with other investments or
                      mutual funds which use a different method to calculate
                      performance.
 
                                   AVERAGE ANNUAL TOTAL RETURN FOR
                            VANGUARD BOND INDEX FUND -- TOTAL BOND MARKET
                                  PORTFOLIO -- INSTITUTIONAL SHARES
 
<TABLE>
<CAPTION>
                               FISCAL PERIODS     TOTAL BOND      AGGREGATE     CONSUMER
                               ENDED 12/31/97  MARKET PORTFOLIO   BOND INDEX   PRICE INDEX
                               --------------  ----------------   ----------   -----------
                               <S>             <C>                <C>          <C>
                               1 Year                9.55%           9.65%        1.70%
                               Lifetime*             7.80            7.74         2.52
</TABLE>
 
                      * September 18, 1995 to December 31, 1997.
 
                                   AVERAGE ANNUAL TOTAL RETURN FOR
                            VANGUARD BOND INDEX FUND -- TOTAL BOND MARKET
                                     PORTFOLIO -- INVESTOR SHARES
 
<TABLE>
<CAPTION>
                               FISCAL PERIODS     TOTAL BOND      AGGREGATE     CONSUMER
                               ENDED 12/31/97  MARKET PORTFOLIO   BOND INDEX   PRICE INDEX
                               --------------  ----------------   ----------   -----------
                               <S>             <C>                <C>          <C>
                               1 Year                9.44%           9.65%        1.70%
                               3 Years              10.24           10.42         2.52
                               5 Years               7.42            7.48         2.60
                               10 Years              8.88            9.18         3.41
                               Lifetime*             8.09            8.51         3.51
</TABLE>
 
                      * December 11, 1986 to December 31, 1997.
- --------------------------------------------------------------------------------
 
DIVIDENDS,
CAPITAL GAINS
AND TAXES
THE PORTFOLIO PAYS
MONTHLY DIVIDENDS     Dividends consisting of virtually all of the ordinary
                      income of the Portfolio are declared daily and are payable
                      to shareholders of record at the time of declaration. Such
                      dividends are paid on the first business day of each
                      month. Capital gains distributions, if any, are made
                      annually. In addition, the Portfolio may occasionally be
                      required to make supplemental dividend or capital gains
                      distributions at some other time during the year.
 
                                       14
<PAGE>   80
 
                      The Portfolio's dividend and capital gains distributions
                      may be reinvested in additional shares or received in
                      cash. See "Choosing a Distribution Option" for a
                      description of these distribution methods. Shareholders
                      who choose to reinvest their dividend distributions will
                      receive a quarterly (not monthly) confirmation statement.
 
                      Pursuant to the Internal Revenue Code, certain dividend
                      and capital gains distributions declared by the Portfolio
                      during December, if received by shareholders by January
                      31, are deemed to have been paid by the Portfolio and
                      received by shareholders on December 31 of the prior year.
 
                      The Portfolio intends to continue to qualify for taxation
                      as a "regulated investment company" under the Internal
                      Revenue Code so that it will not be subject to federal
                      income tax to the extent its income is distributed to
                      shareholders. Dividends paid by the Portfolio from net
                      investment income and net short-term capital gains,
                      whether received in cash or reinvested in additional
                      shares, will be taxable to shareholders as ordinary
                      income. For corporate investors, dividends paid by the
                      Portfolio from net investment income will generally not
                      qualify for the intercorporate dividends-received
                      deduction.
 
   
                      Distributions paid by the Portfolio from long-term capital
                      gains, whether received in cash or reinvested in
                      additional shares, are taxable as long-term capital gains,
                      regardless of the length of time you have owned shares in
                      the Portfolio. Long-term capital gains may be taxed at
                      different rates depending on how long the Portfolio held
                      the securities. Capital gains distributions are made when
                      the Portfolio realizes net capital gains on sales of
                      portfolio securities during the year. Realized capital
                      gains are not expected to be a significant or predictable
                      part of investment return of the Portfolio.
    
 
                      The Portfolio will notify you annually as to the tax
                      status of dividend and capital gains distributions paid by
                      the Portfolio.
 
A CAPITAL GAIN OR
LOSS MAY BE REALIZED
UPON EXCHANGE
OR REDEMPTION         A sale of shares of the Portfolio is a taxable event and
                      may result in a capital gain or loss. A capital gain or
                      loss may be realized from an ordinary redemption of
                      shares, or an exchange of shares between two mutual funds
                      (or two portfolios of a mutual fund).
 
                      Dividend distributions, capital gains distributions, and
                      capital gains or losses from redemptions and exchanges may
                      be subject to state and local taxes.
 
   
                      The Portfolio is required to withhold 31% of taxable
                      dividends, capital gains distributions, and redemptions
                      paid to shareholders who have not complied with IRS
                      taxpayer identification regulations. You may avoid this
                      withholding requirement by certifying on your Account
                      Registration Form your Social Security or employer
                      identification number and by certifying that you are not
                      subject to backup withholding.
    
 
                      The Portfolio has obtained a Certificate of Authority to
                      do business as a foreign corporation in Pennsylvania and
                      does business and maintains an office in that state. In
                      the opinion of counsel, the shares of the Portfolio are
                      exempt from Pennsylvania personal property taxes.
 
                                       15
<PAGE>   81
 
   
                      The tax discussion set forth on page 15 is included for
                      general information only. Prospective investors should
                      consult their own tax advisers concerning the tax
                      consequences of an investment in the Portfolio.
    
- --------------------------------------------------------------------------------
 
THE SHARE PRICE OF
THE PORTFOLIO         The Total Bond Market Portfolio's share price, or "net
                      asset value" per share, is calculated by dividing the net
                      assets attributed to each share class by the total number
                      of shares outstanding for that share class. The net asset
                      value is determined as of the close of trading on the New
                      York Stock Exchange (the "Exchange"), generally 4:00 p.m.
                      Eastern time on each day that the Exchange is open for
                      trading.
 
                      Short term instruments (those with remaining maturities of
                      60 days or less) may be valued at cost, plus or minus any
                      amortized discount or premium, which approximates market
                      value.
 
                      Bonds and other fixed income securities may be valued on
                      the basis of prices provided by a pricing service when
                      such prices are believed to reflect the fair market value
                      of such securities. The prices provided by a pricing
                      service may be determined without regard to bid or last
                      sale prices of each security, but take into account
                      institutional-size transactions in similar groups of
                      securities as well as any developments related to specific
                      securities.
 
                      Other assets and securities for which no quotations are
                      readily available or which are restricted as to sale (or
                      resale) are valued by such methods as the Board of
                      Directors deems in good faith to reflect fair value.
 
   
                      The share price for the Portfolio can be found daily in
                      the mutual fund listings of most major newspapers under
                      the heading of Vanguard Index Funds.
    
- --------------------------------------------------------------------------------
 
   
GENERAL
INFORMATION           The Total Bond Market Portfolio Institutional Shares is a
                      class of shares offered by the Vanguard Bond Index Fund,
                      Inc., a Maryland Corporation. The Articles of
                      Incorporation permit the Directors to issue 2,000,000,000
                      shares of common stock, with a $.001 par value. The Board
                      of Directors has the power to designate one or more
                      portfolios and classes of shares of common stock of such
                      portfolios and to classify or reclassify any unissued
                      shares with respect to such portfolios and classes.
                      Currently the Fund is offering shares of four series. The
                      Total Bond Market Portfolio offers two separate classes of
                      shares; the Total Bond Market Portfolio Investor Shares
                      which is open to investors with a minimum investment of
                      $3,000, and the Total Bond Market Portfolio Institutional
                      Shares which are designed for investors who meet certain
                      administrative criteria and a minimum initial investment
                      of $10 million.
    
 
                      The shares of the Portfolio are fully paid and
                      non-assessable; have no preference as to conversion,
                      exchange, dividends, retirement or other features; and
                      have no pre-emptive rights. Such shares have
                      non-cumulative voting rights, meaning that the holders of
                      more than 50% of the shares voting for the election of
                      Directors can elect 100% of the Directors if they so
                      choose.
 
                                       16
<PAGE>   82
 
                      Annual meetings of shareholders will not be held except as
                      required by the Investment Company Act of 1940 and other
                      applicable law. An annual meeting will be held to vote on
                      the removal of a Director or Directors of the Fund if
                      requested in writing by the holders of not less than 10%
                      of the outstanding shares of the Fund.
 
                      All securities and cash for the Total Bond Market
                      Portfolio are held by Chase Manhattan Bank, New York, NY.
                      CoreStates Bank, N.A., Philadelphia, PA, holds daily cash
                      balances that are used by the Fund's Portfolios to invest
                      in repurchase agreements or securities acquired in these
                      transactions. The Vanguard Group, Inc., Valley Forge, PA,
                      serves as the Fund's Transfer and Dividend Disbursing
                      Agent. Price Waterhouse LLP, serves as independent
                      accountants for the Fund and will audit its financial
                      statements annually. The Fund is not involved in any
                      litigation.
- --------------------------------------------------------------------------------
 
                                       17
<PAGE>   83
 
                               SHAREHOLDER GUIDE
 
OPENING AN
ACCOUNT AND
PURCHASING
SHARES                To open a new account, complete an Account Registration
                      Form and mail it to:
 
<TABLE>
<S>                             <C>
                                                  THE VANGUARD GROUP
                                                  VANGUARD TOTAL BOND MARKET PORTFOLIO
                                                 INSTITUTIONAL SHARES
                                                  ATTN: INSTITUTIONAL INVESTOR SERVICES
                                                  P.O. BOX 1472
                                                  VALLEY FORGE, PA 19482
</TABLE>
 
                      For express or registered mail, send your registration
                      form to: The Vanguard Group, Vanguard Total Bond Market
                      Portfolio Institutional Shares, Attn: Institutional
                      Investor Services, 100 Vanguard Boulevard, Malvern, PA
                      19355.
 
                      Once the account has been opened, Vanguard will assign an
                      Institutional Investor Services Representative for future
                      account transactions.
 
   
                      Shares of the Portfolio may be purchased by Federal Funds
                      wire. The minimum initial investment for the Portfolio is
                      $10 million. Please contact your Institutional Investor
                      Services Representative or call The Vanguard Group at
                      1-800-523-8066 to notify the Portfolio of the intended
                      investment and to receive an account number. Wiring
                      instructions are provided on page 19.
    
 
                      Because of the risks associated with bond investments, the
                      Portfolio is intended to be a long-term investment vehicle
                      and is not designed to provide investors with a means of
                      speculating on short-term bond market movements. Excessive
                      trading results in higher transaction costs paid for by
                      the remaining shareholders. Consequently, the Fund
                      reserves the right to assess a transaction fee (payable to
                      the Portfolio) or to reject any specific purchase (and
                      exchange purchase) request. Shareholders subject to any
                      transaction fee will be notified by the Fund. The Fund
                      also reserves the right to suspend the offering of shares
                      for a period of time.
 
                      The Portfolio's shares are purchased at the
                      next-determined net asset value after your investment has
                      been received. See "When Your Account Will be Credited".
                      The Fund is offered on a no-load basis (i.e., there are no
                      sales commissions or 12b-1 fees).
 
IMPORTANT NOTE
ON EXPENSES           The Portfolio reserves the right to deduct a portfolio
                      transaction fee of 0.18% of the entire purchase from
                      purchases of the shares of the Portfolio which exceed or
                      are expected to exceed $50 million if such purchases are
                      reasonably deemed to be disruptive to efficient portfolio
                      management. The fee will be paid to the Portfolio to
                      offset transaction costs of buying securities. The fee is
                      not paid to Vanguard and is not a sales charge. Purchasers
                      of shares of the Portfolio may determine whether a fee
                      will be charged by calling their Institutional Investor
                      Service Representative in advance of their purchase.
 
                                       18
<PAGE>   84
 
   
<TABLE>
<S>                             <C>                              <C>
                                NEW ACCOUNT                      EXISTING ACCOUNTS
ADDITIONAL                      Please contact your Institu-     Additional investments may be made at any time by
INVESTMENTS                     tional Investor Services         wiring monies to Vanguard. To ensure prompt
                                Representative.                  investment, please notify your Institutional In-
                                                                 vestor Services Representative in advance of the
                                                                 wire.
                                ------------------------------------------------------------------------------------
PURCHASING BY WIRE                              CORESTATES BANK, N.A.
Money should be                                 ABA 031000011
wired to:                                       CORESTATES NO. 0101 9897
                                                ATTN: VANGUARD
BEFORE WIRING                                   VANGUARD BOND INDEX FUND
Please contact your                             TOTAL BOND MARKET PORTFOLIO INSTITUTIONAL SHARES
Institutional Investor                          ACCOUNT NUMBER
Services Representative                         ACCOUNT REGISTRATION
</TABLE>
    
 
                      To assure proper receipt, please be sure your bank
                      includes the name of the Portfolio, the account number
                      Vanguard has assigned to you and the eight-digit
                      CoreStates number. If you are opening a new account,
                      please complete the Account Registration Form and mail it
                      to the "New Account" address above after completing your
                      wire arrangement. NOTE: Federal Funds wire purchase orders
                      will be accepted only when the Fund and Custodian Bank are
                      open for business.
 
PURCHASING BY
EXCHANGE (FROM A
VANGUARD ACCOUNT)     Purchases may also be made by exchange from an existing
                      Vanguard Fund account. However, the Portfolio reserves the
                      right to refuse any exchange purchase request. Please call
                      your Institutional Investor Services Representative or
                      call Participant Services at 1-800-523-8066 for more
                      information.
 
DIVIDEND
DISTRIBUTIONS
                      Dividend distributions paid by the Portfolio will be
                      automatically reinvested in additional Portfolio shares. A
                      cash dividend option is also available from the Portfolio.
                      Please contact your Institutional Investor Services
                      Representative for further information.
 
CERTIFICATES
                      Share certificates will not be issued for the Portfolio.
 
ELECTRONIC
PROSPECTUS
DELIVERY
                      You may receive a prospectus for the Fund or any of the
                      Vanguard Funds in an electronic format through Vanguard's
                      website at www.vanguard.com. For additional information
                      please see "Other Vanguard Services -- Computer Access."
- --------------------------------------------------------------------------------
 
DIVIDEND AND
TRADE DATE POLICY     Investments will qualify for dividends on the date of
                      purchase under the following conditions:
 
                      - FOR INVESTMENTS OF $5 MILLION OR MORE: The Portfolio
                        must be notified of the intended purchase by 4:00 p.m.
                        (Eastern time) on the prior business day and the Federal
                        Funds wire must be received by Vanguard by 4:00 p.m.
                        (Eastern time) on the day of purchase.
 
                                       19
<PAGE>   85
 
                      - FOR INVESTMENTS OF LESS THAN $5 MILLION: The Portfolio
                        must be notified of the intended purchase by 10:45 a.m.
                        (Eastern time) on the day of purchase and the Federal
                        Funds wire must be received by 4:00 p.m. (Eastern time).
 
                      Generally, if these requirements are not met, an
                      investment will begin to earn dividends on the business
                      day following receipt of a Federal Funds wire.
 
WHEN YOUR ACCOUNT
WILL BE CREDITED      The trade date, the day on which an account is credited,
                      is generally the day on which the Portfolio receives an
                      investment in the form of Federal Funds. For purchases by
                      Federal Funds wire or by exchange, the Portfolio is
                      credited immediately with Federal Funds. If a purchase by
                      Federal Funds wire or exchange is received by the close of
                      trading on the New York Stock Exchange (the "Exchange"),
                      generally 4:00 p.m. Eastern time, the trade date is the
                      day of receipt. If a purchase is received after the close
                      of the Exchange, the trade date is the business day
                      following the receipt of the wire or exchange.
 
                      The Portfolio reserves the right to suspend the offering
                      of shares for a period of time. The Portfolio also
                      reserves the right to reject any specific purchase
                      request.
- --------------------------------------------------------------------------------
 
SELLING SHARES
WIRE PROCEEDS         Any portion of an account may be withdrawn by contacting
                      your Institutional Investor Services Representative. The
                      redemption proceeds will be wired to the bank account
                      indicated on the Account Registration Form on the business
                      day following receipt of a request.
 
                      For a redemption of an entire account balance, accrued
                      dividends will not be included in the initial redemption
                      wire, but will be sent separately by check or wire.
 
                      Wire redemptions of less than $5,000 are subject to a $5
                      charge deducted from the principal in your account. There
                      is no charge for wire redemptions of $5,000 or more, or
                      for subsequent dividend wires.
 
                      For our mutual protection, wiring instructions must be on
                      file at Vanguard prior to executing any redemption
                      request. A request to change the bank account associated
                      with the wire redemption feature or a request to wire
                      funds to a bank other than that on file must be received
                      in writing. A signature guarantee of an authorized officer
                      is required if the bank registration is not identical to
                      the Vanguard Fund account registration.
- --------------------------------------------------------------------------------
SELLING BY EXCHANGE   Shares may also be sold by making an exchange to another
                      Vanguard Fund account. For further information, please
                      contact your Institutional Investor Services
                      Representative.
- --------------------------------------------------------------------------------
OTHER REDEMPTION
INFORMATION
                      The Portfolio may suspend the redemption rights or
                      postpone payment at times when the New York Stock Exchange
                      is closed or under any emergency circumstances as
                      determined by the United States Securities and Exchange
                      Commission.
- --------------------------------------------------------------------------------
 
                                       20
<PAGE>   86
 
REQUIRED
CONVERSION TO
INVESTOR
SHARE CLASS           The Portfolio reserves the right to convert an investor's
                      Total Bond Market Portfolio Institutional Shares into
                      Total Bond Market Portfolio Investor Shares if the
                      investor's account balance falls below $10 million. Any
                      such conversion will be preceded by written notice to the
                      investor.
- --------------------------------------------------------------------------------
 
EXCHANGING
SHARES                Shares of the Portfolio may be exchanged for those of
                      other available Vanguard Portfolios or classes of
                      Portfolios either by telephone or mail. Contact your
                      Institutional Investor Services Representative for further
                      information. Telephone exchange requests must ordinarily
                      be received by the close of trading on the Exchange in
                      order to be processed on the date of receipt. The new Fund
                      account will bear the identical registration of the
                      Vanguard Total Bond Market Portfolio Institutional Shares
                      account.
 
                      Telephone exchanges are not permitted for several Vanguard
                      Funds, and there also may be restrictions on new
                      investments in certain Funds. Large exchange requests
                      (i.e., those over $250,000) require prior approval by
                      Vanguard on behalf of the Fund. Contact your Institutional
                      Investor Services Representative for full information,
                      including a prospectus.
 
                      Neither the Portfolio nor Vanguard is responsible for the
                      authenticity of exchange instructions received by
                      telephone. Every effort will be made to maintain the
                      exchange privilege. However, the Portfolio reserves the
                      right to revise or terminate its provisions, limit the
                      amount of, or reject any exchange, as deemed necessary, at
                      any time.
- --------------------------------------------------------------------------------
 
IMPORTANT
INFORMATION
ABOUT TELEPHONE
TRANSACTIONS          The ability to initiate redemptions (except wire or Fund
                      Express redemptions) and exchanges by telephone is
                      automatically established on your account unless you
                      request in writing that telephone transactions on your
                      account not be permitted. The ability to initiate wire
                      redemptions by telephone will be established on your
                      account only if you specifically elect this option in
                      writing.
 
                      To protect your account from losses resulting from
                      unauthorized or fraudulent telephone instructions,
                      Vanguard adheres to the following security procedures:
 
                      1. SECURITY CHECK.  To request a transaction by telephone,
                         the caller must know (i) the name of the Portfolio;
                         (ii) the 10-digit account number; (iii) the exact name
                         and address used in the registration; and (iv) the
                         Social Security or employer identification number
                         listed on the account.
 
                      2. PAYMENT POLICY.  The proceeds of any telephone
                         redemption by mail will be made payable to the
                         registered shareowner and mailed to the address of
                         record only. In the case of a telephone redemption by
                         wire, the wire transfer will be made only in accordance
                         with the shareowner's prior written instructions.
 
                      Neither the Portfolio nor Vanguard will be responsible for
                      the authenticity of transaction instructions received by
                      telephone, provided that reasonable security procedures
                      have been followed. Vanguard believes that the security
                      procedures described above are reasonable, and that if
                      such procedures are followed, you will
 
                                       21
<PAGE>   87
 
                      bear the risk of any losses resulting from unauthorized or
                      fraudulent telephone transactions on your account.
- --------------------------------------------------------------------------------
 
OTHER ACCOUNT
INFORMATION           For corporate investors, a current corporate resolution
                      must be maintained on file at Vanguard at all times. The
                      initial application serves as a corporate resolution. Any
                      revisions to a corporate resolution must be submitted to
                      your Institutional Investor Services Representative at
                      Vanguard.
 
                      To change the registration of an account, a request must
                      be submitted in writing to Vanguard and include the
                      following information: the account number and portfolio
                      name; authorized signatures; any applicable signature
                      guarantees; and other supporting legal documents as
                      necessary.
 
                      All requests should be mailed to the following address:
 
                                  THE VANGUARD GROUP
                                  ATTN: INSTITUTIONAL INVESTOR SERVICES
                                  P.O. BOX 1472
                                  VALLEY FORGE, PA 19482
- --------------------------------------------------------------------------------
 
OTHER VANGUARD
SERVICES
COMPUTER ACCESS
VANGUARD ONLINE
WWW.VANGUARD.COM      Use your personal computer to learn more about Vanguard's
                      funds and services; keep in touch with your Vanguard
                      accounts; map out a long-term investment strategy;
                      initiate certain transactions; and ask questions, make
                      suggestions, and send messages to Vanguard.
 
                      Our education-oriented website provides timely news and
                      information about Vanguard's funds and services; an online
                      "university" that offers a variety of mutual fund classes;
                      and easy-to-use, interactive tools to help you create your
                      own investment and retirement strategies.
- --------------------------------------------------------------------------------
 
                                       22
<PAGE>   88
 
                      [THIS PAGE INTENTIONALLY LEFT BLANK]
<PAGE>   89
 
                      [THIS PAGE INTENTIONALLY LEFT BLANK]
<PAGE>   90
 
                      [THIS PAGE INTENTIONALLY LEFT BLANK]
<PAGE>   91
 
- --------------------------------------------------------------------------------
 
<TABLE>
<S>       <C>                                   <C>
      I222LOGO
          ----------------------------
          THE VANGUARD GROUP
          Institutional Investor Service
          P.O. Box 2900
          Valley Forge, PA 19482
          INSTITUTIONAL PARTICIPANT
          SERVICES DEPARTMENT:
          1-800-523-8066
          TRANSFER AGENT:
          The Vanguard Group, Inc.
          P.O. Box 2900
          Valley Forge, PA 19482
</TABLE>
 
- --------------------------------------------------------------------------------
<PAGE>   92
 
                                     PART B
 
                            VANGUARD BOND INDEX FUND
 
                      STATEMENT OF ADDITIONAL INFORMATION
 
                                 APRIL 17, 1998
 
     This Statement is not a prospectus, but should be read in conjunction with
the Fund's current Prospectus (dated April 17, 1998). To obtain the Prospectus
please call:
 
                      VANGUARD INVESTOR INFORMATION CENTER
                                 1-800-662-7447
 
                               TABLE OF CONTENTS
 
<TABLE>
<CAPTION>
                                                              PAGE
                                                              ----
<S>                                                           <C>
Investment Policies.........................................     1
Investment Limitations......................................     4
Yield and Total Return......................................     6
Purchase of Shares..........................................     6
Redemption of Shares........................................     7
Management of the Fund......................................     8
Portfolio Transactions......................................    11
Performance Measures........................................    11
Financial Statements........................................    13
Appendix -- Description of Bond Ratings.....................    13
</TABLE>
 
                              INVESTMENT POLICIES
 
     REPURCHASE AGREEMENTS  Each Portfolio of the Fund may invest in repurchase
agreements with commercial banks, brokers or dealers to generate income from its
excess cash balances. A repurchase agreement is an agreement under which a
Portfolio acquires a money market instrument (generally a security issued by the
U.S. Government or an agency thereof, a banker's acceptance or a certificate of
deposit) from a Federal Reserve member bank with minimum assets of at least $2
billion or a registered securities dealer, subject to resale to the seller at an
agreed upon price and date (normally, the next business day). A repurchase
agreement may be considered a loan collateralized by securities. The resale
price reflects an agreed upon interest rate effective for the period the
instrument is held by a Portfolio and is unrelated to the interest rate on the
underlying instrument. In these transactions, the securities acquired by a
Portfolio (including accrued interest earned thereon) must have a total value in
excess of the value of the repurchase agreement and are held by a custodian bank
until repurchased. In addition, the Fund's Board of Directors will monitor each
Portfolio's repurchase agreement transactions generally and will establish
guidelines and standards for review of the creditworthiness of any bank, broker
or dealer party to a repurchase agreement with a Portfolio. No more than an
aggregate of 15% of a Portfolio's assets, at the time of investment, will be
invested in repurchase agreements having maturities longer than seven days and
securities subject to legal or contractual restrictions on resale, or for which
there are no readily available market quotations. From time to time, the Fund's
Board of Directors may determine that certain restricted securities known as
Rule 144A securities are liquid and not subject to the 15% limitation described
above.
 
     The use of repurchase agreements involves certain risks. For example, if
the other party to the agreement defaults on its obligation to repurchase the
underlying security at a time when the value of the security has declined, a
Portfolio may incur a loss upon disposition of the security. If the other party
to the agreement becomes insolvent and subject to liquidation or reorganization
under the Bankruptcy Code or other laws, a court may determine that the
underlying security is collateral for a loan by a Portfolio not within its
control and therefore the Portfolio may not be able to substantiate its interest
in the underlying security and may be
 
                                        1
<PAGE>   93
 
deemed an unsecured creditor of the other party to the agreement. While the
Fund's management acknowledges these risks, it is expected that they can be
controlled through careful monitoring procedures.
 
     LENDING OF SECURITIES  Each Portfolio of the Fund may lend its securities
to qualified institutional investors who need to borrow securities in order to
complete certain transactions, such as covering short sales, avoiding failures
to deliver securities or completing arbitrage operations. By lending its
portfolio securities, a Portfolio attempts to increase its net investment income
through the receipt of interest on the loan. Any gain or loss in the market
price of the securities loaned that might occur during the term of the loan
would be for the account of the Portfolio. A Portfolio may lend its portfolio
securities to qualified brokers, dealers, banks or other financial institutions,
so long as the terms, the structure and the aggregate amount of such loans are
not inconsistent with the Investment Company Act of 1940, or the Rules and
Regulations or interpretations of the Securities and Exchange Commission (the
"Commission") thereunder, which currently require that: (a) the borrower pledge
and maintain with a Portfolio collateral consisting of cash, a letter of credit
issued by a domestic U.S. bank, or securities issued or guaranteed by the United
States Government having at all times not less than 100% of the value of the
securities loaned, (b) the borrower add to such collateral whenever the price of
the securities loaned rises (i.e. the borrower "marks to the market" on a daily
basis), (c) the loan be made subject to termination by a Portfolio at any time,
and (d) the Portfolio receive reasonable interest on the loan (which may include
the Portfolio's investing any cash collateral in interest bearing short-term
investments), any distribution on the loaned securities and any increase in
their market value. Loan arrangements made by a Portfolio will comply with all
other applicable regulatory requirements, including the rules of the New York
Stock Exchange, which rules presently require the borrower, after notice, to
redeliver the securities within the normal settlement time of three business
days. All relevant facts and circumstances, including the creditworthiness of
the broker, dealer or institution, will be considered in making decisions with
respect to the lending of securities, subject to review by the Fund's Board of
Directors.
 
     At the present time, the Staff of the Commission does not object if an
investment company pays reasonable negotiated fees in connection with loaned
securities, so long as such fees are set forth in a written contract and
approved by the investment company's Directors. In addition, voting rights pass
with the loaned securities, but if a material event will occur affecting an
investment on loan, the loan must be called and the securities voted.
 
     FUTURES CONTRACTS AND OPTIONS  Each Portfolio of the Fund may enter into
futures contracts, options, and options on futures contracts for the purpose of
remaining fully invested and reducing transaction costs. Futures contracts
provide for the future sale by one party and purchase by another party of a
specified amount of a specific security at a specified future time and at a
specified price. Futures contracts which are standardized as to maturity date
and underlying financial instrument are traded on national futures exchanges.
Futures exchanges and trading are regulated under the Commodity Exchange Act by
the Commodity Futures Trading Commission ("CFTC"), a U.S. Government agency.
Assets committed to futures contracts will be segregated at the Fund's custodian
bank to the extent required by law.
 
     Although futures contracts by their terms call for actual delivery or
acceptance of the underlying securities, in most cases the contracts are closed
out before the settlement date without the making or taking of delivery. Closing
out an open futures position is done by taking an opposite position ("buying" a
contract which has previously been "sold," or "selling" a contract previously
purchased) in an identical contract to terminate the position. Brokerage
commissions are incurred when a futures contract is bought or sold.
 
     Futures traders are required to make a good faith initial margin deposit in
cash or securities with a broker or custodian to initiate and maintain open
positions in futures contracts. A margin deposit is intended to assure
completion of the contract (delivery or acceptance of the underlying security)
if it is not terminated prior to the specified delivery date. Minimal initial
margin requirements are established by the futures exchange and may be changed.
Brokers may establish deposit requirements which are higher than the exchange
minimums. Futures contracts are customarily purchased and sold with deposits
that may range upward from less than 5% of the value of the contract being
traded. A Portfolio's initial margin requirement is ordinarily in the form of
portfolio securities. These securities are segregated in a separate custody
account at the Portfolio's custodian bank; they are not delivered to the futures
dealer.
 
                                        2
<PAGE>   94
 
     After a futures contract position is opened, the value of the contract is
marked to market daily. If the futures contract price changes to the extent that
the margin on deposit does not satisfy margin requirements, payment of
additional "variation" margin will be required. Conversely, change in the
contract value may reduce the required margin, resulting in a repayment of
excess margin to the contract holder. Variation margin payments are made to and
from the futures broker for as long as the contract remains open. A Portfolio
expects to earn interest income on its initial margin deposits.
 
     Traders in futures contracts may be broadly classified as either "hedgers"
or "speculators." Hedgers use the futures markets primarily to offset
unfavorable changes in the value of securities otherwise held for investment
purposes or expected to be acquired by them. Speculators are less inclined to
own the securities underlying the futures contracts which they trade, and use
futures contracts with the expectation of realizing profits from fluctuations in
the prices of underlying securities. The Portfolios intend to use futures
contracts only for bona fide hedging purposes.
 
     Regulations of the CFTC applicable to the Fund require that all of its
futures transactions constitute bona fide hedging transactions except to the
extent that the aggregate initial margins and premiums required to establish any
non-hedging positions do not exceed five percent of the value of the Fund's
portfolio. A Portfolio will only sell futures contracts to protect securities it
owns against price declines or purchase contracts to protect against an increase
in the price of securities it intends to purchase. As evidence of this hedging
interest, a Portfolio expects that approximately 75% of its futures contract
purchases will be "completed," that is, equivalent amounts of related securities
will have been purchased or are being purchased by a Portfolio upon sale of open
futures contracts.
 
     Although techniques other than the sale and purchase of futures contracts
could be used to control a Portfolio's exposure to market fluctuations, the use
of futures contracts may be a more effective means of hedging this exposure.
While a Portfolio will incur commission expenses in both opening and closing out
futures positions, these costs are lower than transaction costs incurred in the
purchase and sale of the underlying securities.
 
     RESTRICTIONS ON THE USE OF FUTURES CONTRACTS  A Portfolio will not enter
into futures contract transactions to the extent that, immediately thereafter,
the sum of its initial margin deposits on open contracts exceeds 5% of the
market value of its total assets. In addition, a Portfolio will not enter into
futures contracts to the extent that its outstanding obligations to purchase
securities under these contracts would exceed 20% of its total assets. Assets
committed to futures contracts or options will be held in a segregated account
at the Portfolio's custodian bank.
 
     RISK FACTORS IN FUTURES TRANSACTIONS  Positions in futures contracts may be
closed out only on an Exchange which provides a secondary market for such
futures. However, there can be no assurance that a liquid secondary market will
exist for any particular futures contract at any specific time. Thus, it may not
be possible to close a futures position. In the event of adverse price
movements, a Portfolio would continue to be required to make daily cash payments
to maintain its required margin. In such situations, if a Portfolio has
insufficient cash, it may have to sell portfolio securities to meet daily margin
requirements at a time when it may be disadvantageous to do so. In addition, a
Portfolio may be required to make delivery of the instruments underlying futures
contracts it holds. The inability to close options and futures positions also
could have an adverse impact on the ability to hedge it effectively.
 
     A Portfolio will minimize the risk that it will be unable to close out a
futures contract by only entering into futures which are traded on national
futures exchanges and for which there appears to be a liquid secondary market.
 
     The risk of loss in trading futures contracts in some strategies can be
substantial, due both to the low margin deposits required, and the extremely
high degree of leverage involved in futures pricing. As a result, a relatively
small price movement in a futures contract may result in immediate and
substantial loss (as well as gain) to the investor. For example, if at the time
of purchase, 10% of the value of the futures contract is deposited as margin, a
subsequent 10% decrease in the value of the futures contract would result in a
total loss of the margin deposit, before any deduction for the transaction
costs, if the account were then closed out.
 
                                        3
<PAGE>   95
 
A 15% decrease would result in a loss equal to 150% of the original margin
deposit if the contract were closed out. Thus, a purchase or sale of a futures
contract may result in losses in excess of the amount invested in the contract.
However, because the futures strategies of the Fund are engaged in only for
hedging purposes, the Adviser does not believe that the Portfolios are subject
to the risks of loss frequently associated with futures transactions. A
Portfolio would presumably have sustained comparable losses if, instead of the
futures contract, it had invested in the underlying financial instrument and
sold it after the decline.
 
     Utilization of futures transactions by a Portfolio does involve the risk of
imperfect or no correlation where the securities underlying futures contracts
have different maturities than the portfolio securities being hedged. It is also
possible that a Portfolio could both lose money on futures contracts and also
experience a decline in value of its portfolio securities. There is also the
risk of loss by a Portfolio of margin deposits in the event of bankruptcy of a
broker with whom a Portfolio has an open position in a futures contract or
related option. Additionally, investments in futures contracts and options
involve the risk that the investment adviser will incorrectly predict stock
market and interest rate trends.
 
     Most futures exchanges limit the amount of fluctuation permitted in futures
contract prices during a single trading day. The daily limit establishes the
maximum amount that the price of a futures contract may vary either up or down
from the previous day's settlement price at the end of a trading session. Once
the daily limit has been reached in a particular type of contract, no trades may
be made on that day at a price beyond that limit. The daily limit governs only
price movement during a particular trading day and therefore does not limit
potential losses, because the limit may prevent the liquidation of unfavorable
positions. Futures contract prices have occasionally moved to the daily limit
for several consecutive trading days with little or no trading, thereby
preventing prompt liquidation of future positions and subjecting some futures
traders to substantial losses.
 
     FEDERAL TAX TREATMENT OF FUTURES CONTRACTS  A Portfolio is required for
federal income tax purposes to recognize as income for each taxable year its net
unrealized gains and losses on certain futures contracts as of the end of the
year as well as those actually realized during the year. In most cases, any gain
or loss recognized with respect to a futures contract is considered to be 60%
long-term capital gain or loss and 40% short-term capital gain or loss, without
regard to the holding period of the contract. Furthermore, sales of futures
contracts which are intended to hedge against a change in the value of
securities held by a Portfolio may affect the holding period of such securities
and, consequently, the nature of the gain or loss on such securities upon
disposition. A Portfolio may be required to defer the recognition of losses on
futures contracts to the extent of any unrecognized gains on related positions
held by the Portfolio.
 
     In order for a Portfolio to continue to qualify for Federal income tax
treatment as a regulated investment company, at least 90% of its gross income
for a taxable year must be derived from qualifying income; i.e., dividends,
interest, income derived from loans of securities, gains from the sale of
securities or of foreign currencies or other income derived with respect to a
Portfolio's business of investing in securities. It is anticipated that any net
gain realized from the closing out of futures contracts will be considered gain
from the sale of securities and therefore be qualifying income for purposes of
the 90% requirement.
 
     A Portfolio will distribute to shareholders annually any net capital gains
which have been recognized for federal income tax purposes (including unrealized
gains at the end of a Portfolio's fiscal year) on futures transactions. Such
distributions will be combined with distributions of capital gains realized on a
Portfolio's other investments and shareholders will be advised on the nature of
the distributions.
 
                             INVESTMENT LIMITATIONS
 
     The following restrictions and fundamental policies cannot be changed
without approval of the holders of a majority of the outstanding shares of a
Portfolio (as defined in the Investment Company Act of 1940). Each Portfolio may
not:
 
      1) change its investment objective without shareholder approval, which is
         to duplicate the total investment return (capital change plus income)
         of publicly-traded investment grade fixed-income securities by
         attempting to duplicate the investment performance of an investment
         grade bond index using index matching and index sampling techniques;
                                        4
<PAGE>   96
 
      2) invest in commodities or purchase real estate, although it may purchase
         and sell interest rate futures contracts;
 
      3) purchase securities on margin or sell securities short (the deposit or
         payment by a Portfolio of initial or variation margin in order to
         engage in an interest-rate futures contract is not considered the
         purchase of a security on margin);
 
      4) purchase more than 5% of the outstanding voting securities of any
         company;
 
      5) invest more than 5% of the value of its total assets in the securities
         of any single issuer except obligations of the U.S. Government and its
         instrumentalities;
 
      6) borrow money, except that a Portfolio may borrow from banks (or through
         reverse repurchase agreements), for temporary or emergency (not
         leveraging) purposes, including the meeting of redemption requests
         which might otherwise require the untimely disposition of securities,
         in an amount not exceeding 15% of the value of a Portfolio's total
         assets (including the amount borrowed) at the time the borrowing is
         made. Whenever borrowings exceed 5% of the value of a Portfolio's total
         assets, a Portfolio will not make any additional investments;
 
      7) pledge, mortgage, or hypothecate any of its assets to an extent greater
         than 5% of the value of its total assets;
 
      8) issue senior securities. Collateral arrangements with regard to initial
         and variation margin on interest-rate futures contracts shall not be
         considered issuance of a senior security;
 
      9) engage in the business of underwriting securities issued by other
         persons, except to the extent that a Portfolio may technically be
         deemed to be an underwriter under the Securities Act of 1933, as
         amended, in disposing of portfolio securities;
 
     10) purchase or otherwise acquire any security if, as a result, more than
         15% of its net assets (including any investment in The Vanguard Group,
         Inc.) would be invested in securities that are illiquid;
 
     11) invest for the purpose of controlling management of any company;
 
     12) invest in securities of other investment companies, except as they may
         be acquired as a part of a merger, consolidation or acquisition of
         assets or otherwise to the extent permitted by Section 12 of the 1940
         Act. A Portfolio will invest only in investment companies which have
         investment objectives and investment policies consistent with those of
         the Portfolio;
 
     13) have dealings on behalf of a Portfolio with Officers and Directors of
         the Fund, except for the purchase or sale of securities on an agency or
         commission basis;
 
     14) make loans to any Officers, Directors or employees of the Fund;
 
     15) invest in assessable securities or securities involving unlimited
         liability on the part of the holders thereof;
 
     16) make loans except (i) by purchasing bonds, debentures or similar
         obligations (including repurchase agreements, which are either publicly
         distributed or customarily purchased by institutional investors) and
         (ii) by lending its securities to banks, brokers, dealers and other
         financial institutions so long as such loans are not inconsistent with
         the Investment Company Act or the Rules and Regulations or
         interpretations of the Commission thereunder;
 
     17) invest directly in oil, gas or other mineral exploration or development
         programs.
 
     The investment limitations set forth above are considered at the time that
a Portfolio purchases securities. Notwithstanding these limitations, a Portfolio
may own all or any portion of the securities of, or make loans to, or contribute
to the costs or other financial requirements of any company which will be wholly
owned by the Fund and one or more other investment companies and is primarily
engaged in the business of providing, at-cost, management, administrative,
distribution or related services to the Fund and other investment companies.
(See "The Vanguard Group.") As a non-fundamental policy, the Fund will not
invest more
 
                                        5
<PAGE>   97
 
than 5% of its assets in the securities of companies that, together with
predecessors, have been in continuous operation for less than three years.
 
                             YIELD AND TOTAL RETURN
 
     The yield of the Total Bond Market Portfolio for the 30-day period ended
December 31, 1997 was +6.22%. The yield of the Short-Term Bond,
Intermediate-Term Bond, Long-Term Bond and the Total Bond Market Portfolio
Institutional Shares Portfolios for the 30-day period ended December 31, 1997
was +5.77%, +6.09%, +6.21% and +6.32%, respectively. Yields are calculated daily
and premiums and discounts on asset-backed securities are not amortized.
 
     The average annual total return of the Total Bond Market Portfolio for the
one- and five-year periods ended December 31, 1997 and since its inception on
December 11, 1986 was 9.44%*, 7.42%* and 8.88%*, respectively. The average
annual total return of the Short-Term Bond Portfolio for the one-year period
ended December 31, 1997 and since its inception on March 1, 1994 was 7.04%* and
6.18%*. The average annual total return of the Intermediate-Term Bond Portfolio
for the one-year period ended December 31, 1997 and since its inception on March
1, 1994 was 9.41%* and 7.49%*. The average annual total return of the Long-Term
Bond Portfolio for the one-year period ended December 31, 1997 and since its
inception on March 1, 1994 was 14.30%* and 9.41%*. The average annual total
return of the Total Bond Market Portfolio Institutional Shares Portfolio for the
one-year period ended December 31, 1997 and since its inception on September 18,
1995 was 9.55% and 7.80%. Total return is computed by finding the average
compounded rates of return over the one-year, five-year and since inception
periods set forth above that would equate an initial amount invested at the
beginning of the periods to the ending redeemable value of the investment.
 
     *Performance figures are not adjusted for the annual account maintenance
fee of $10.
 
                               PURCHASE OF SHARES
 
     The Fund reserves the right in its sole discretion (i) to suspend the
offerings of its shares, (ii) to reject purchase orders when in the judgment of
management such rejection is in the best interest of the Fund, and (iii) to
reduce or waive the minimum investment for or any other restrictions on initial
and subsequent investments as well as redemption fees for certain fiduciary
accounts or under circumstances where certain economies can be achieved in sales
of a Portfolio's shares. The Fund reserves the right to impose a transaction fee
on purchases of Portfolio shares totaling more than $5 million made during any
six-month period. Such fee would be payable to the Portfolio to offset the
transaction cost associated with securities investments.
 
     The Fund reserves the right to deduct a portfolio transaction fee from
purchases of the shares of each Portfolio. Fees will not be charged on any
investment where the aggregate balance is expected to be less than $50 million
for the Total Bond Market Portfolio; $15 million for the Short-Term Bond
Portfolio; $15 million for the Intermediate-Term Bond Portfolio; and $2 million
for the Long-Term Bond Portfolio. Fees may be charged on the entire lump-sum
purchase for transactions that exceed or are expected to exceed over the next
twelve months the amount indicated for each Portfolio if such purchases are
reasonably deemed to be disruptive to efficient portfolio management. Lump-sum
purchases exceeding the indicated amount for each Portfolio may be considered
disruptive, for example, if the portfolio manager incurs significant transaction
costs in purchasing portfolio securities needed to match the investment
performance of the respective benchmark index. If such purchases can be offset
by redemptions of shares by other shareholders, such fee may be waived or
reduced. A prospective investor may determine whether a fee will be charged by
calling his/her client representative or plan sponsor in advance of his/her
purchase. The fee, if imposed, will be 0.18% for the Total Bond Market
Portfolio; 0.23% for the Intermediate-Term Bond Portfolio; 0.15% for the
Short-Term Bond Portfolio; and 0.20% for the Long-Term Bond Portfolio. The fees
are based on the portfolio manager's estimate of transaction costs, which
depends on the types of securities in which each Portfolio invests.
 
                                        6
<PAGE>   98
 
                              REDEMPTION OF SHARES
 
     The Fund may suspend redemption privileges or postpone the date of payment
(i) during any period that the New York Stock Exchange is closed, or trading on
the Exchange is restricted as determined by the Securities and Exchange
Commission (the "Commission"), (ii) during any period when an emergency exists
as defined by the rules of the Commission as a result of which it is not
reasonably practicable for the Portfolio to dispose of securities owned by it,
or fairly to determine the value of its assets, and (iii) for such other periods
as the Commission may permit.
 
     Each Portfolio has made an election with the Commission to pay in cash all
redemptions requested by any shareholder of record limited in amount during any
90-day period to the lesser of $250,000 or 1% of the net assets of the Portfolio
at the beginning of such period. Such commitment is irrevocable without the
prior approval of the Commission. Redemptions in excess of the above limits may
be paid in whole or in part, in investment securities or in cash, as the
Directors may deem advisable; however, payment will be made wholly in cash
unless the Directors believe that economic or market conditions exist which
would make such a practice detrimental to the best interests of the Fund. If
redemptions are paid in investment securities, such securities will be valued as
set forth in the Prospectus under "The Share Price of Each Portfolio" and a
redeeming shareholder would normally incur brokerage expenses if he converted
these securities to cash.
 
     No charge is made by the Portfolio for redemptions. Any redemption may be
more or less than the shareholder's cost depending on the market value of the
securities held by a Portfolio.
 
                                        7
<PAGE>   99
 
                             MANAGEMENT OF THE FUND
 
DIRECTORS AND OFFICERS
 
     The Officers of the Fund manage its day-to-day operations and are
responsible to the Fund's Board of Directors. The Directors set broad policies
for the Fund and choose its Officers. The following is a list of the Directors
and Officers of the Fund and a statement of their present positions and
principal occupations during the past five years. The mailing address of the
Directors and Officers of the Fund is Post Office Box 876, Valley Forge, PA
19482.
 
JOHN C. BOGLE, (DOB: 5/8/1929)
Senior Chairman and Director*
  Senior Chairman and Director of The Vanguard Group, Inc., and of each of the
  investment companies in The Vanguard Group; Director of The Mead Corporation,
  General Accident Insurance, and Chris-Craft Industries, Inc.
 
JOHN J. BRENNAN, (DOB: 7/29/1954)
Chairman, Chief Executive Officer and Director*
  Chairman, Chief Executive Officer and Director of The Vanguard Group, Inc. and
  of each of the investment companies in The Vanguard Group.
 
ROBERT E. CAWTHORN, (DOB: 9/28/1935)
Director
  Chairman Emeritus and Director of Rhone-Poulenc Rorer, Inc.; Managing Director
  of Global Health Care Partners/DLJ Merchant Banking Partners; Director of Sun
  Company, Inc., and Westinghouse Electric Corporation.
 
BARBARA BARNES HAUPTFUHRER,
(DOB: 10/11/1928) Director
  Director of The Great Atlantic and Pacific Tea Company, KON Office Solutions,
  Inc., Raytheon Company, Knight-Ridder Inc., Massachusetts Mutual Life
  Insurance Co., and Ladies Professional Golf Association; and Trustee Emerita
  of Wellesley College.
 
BRUCE K. MACLAURY, (DOB: 5/7/1931)
Director
  President Emeritus of The Brookings Institution; Director of American Express
  Bank, Ltd., The St. Paul Companies, Inc., and National Steel Corporation.
 
BURTON G. MALKIEL, (DOB: 8/28/1932)
Director
  Chemical Bank Chairman's Professor of Econom-ics, Princeton University;
  Director of Prudential Insurance Co. of America, Amdahl Corporation, Baker
  Fentress & Co., The Jeffrey Co., and South-ern New England Telecommunications
  Company.
 
ALFRED M. RANKIN, JR., (DOB: 10/8/1941)
Director
  Chairman, President, Chief Executive Officer, and Director of NACCO
  Industries, Inc.; Director of The BFGoodrich Company, and The Standard
  Products Company.
 
JOHN C. SAWHILL, (DOB: 6/12/1936)
Director
  President and Chief Executive Officer of The Nature Conservancy; formerly,
  Director and Senior Partner of McKinsey & Co., and President of New York
  University; Director of Pacific Gas and Electric Company, Procter & Gamble,
  and NACCO Industries.
 
JAMES O. WELCH, JR., (DOB: 5/13/1931)
Director
  Retired Chairman of Nabisco Brands, Inc.; retired Vice Chairman and Director
  of RJR Nabisco; Director of TECO Energy, Inc.; and Kmart Corporation.
 
J. LAWRENCE WILSON, (DOB: 3/2/1936)
Director
  Chairman and Chief Executive Officer of Rohm & Haas Company; Director of
  Cummins Engine Company and The Mead Corporation; and Trustee of Vanderbilt
  University.
 
RAYMOND J. KLAPINSKY, (DOB: 12/7/1938)
Secretary*
  Managing Director and Secretary of The Vanguard Group, Inc.; Secretary of each
  of the investment companies in The Vanguard Group.
 
RICHARD F. HYLAND, (DOB: 3/22/1937)
Treasurer*
  Treasurer of The Vanguard Group, Inc. and of each of the investment companies
  in The Vanguard Group.
 
KAREN E. WEST, (DOB: 9/13/1946)
Controller*
  Principal of The Vanguard Group, Inc.; Controller of each of the investment
  companies in The Vanguard Group.
- ---------------
 
*Officers of the Fund are "interested persons" as defined in the Investment
 Company Act of 1940.
 
                                        8
<PAGE>   100
 
     THE VANGUARD GROUP  Vanguard Bond Index Fund is a member of The Vanguard
Group of Investment Companies which consists of more than 30 investment
companies.
 
     Through their jointly-owned subsidiary, The Vanguard Group, Inc.
("Vanguard"), the Fund and the other Funds in the Group obtain at cost virtually
all of their corporate management, administrative and distribution services.
Vanguard also provides investment advisory services on an at-cost basis to
certain Vanguard Funds.
 
     Vanguard employs a supporting staff of management and administrative
personnel needed to provide the requisite services to the Funds and also
furnishes the Funds with necessary office space, furnishings and equipment. Each
Fund pays its share of Vanguard's net expenses which are allocated among the
Funds under methods approved by the Board of Directors (Trustees) of each Fund.
In addition, each Fund bears its own direct expenses such as legal, auditing and
custodian fees.
 
     The Fund's Officers are also Officers and employees of Vanguard. No Officer
or employee owns, or is permitted to own, any securities of any external adviser
for the Funds.
 
     The Vanguard Group adheres to a Code of Ethics established pursuant to Rule
17j-1 under the Investment Company Act of 1940. The Code is designed to prevent
unlawful practices in connection with the purchase or sale of securities by
persons associated with Vanguard. Under Vanguard's Code of Ethics certain
Officers and employees of Vanguard who are considered access persons are
permitted to engage in personal securities transactions. However, such
transactions are subject to procedures and guidelines substantially similar to
those recommended by the mutual fund industry and approved by the U.S.
Securities and Exchange Commission.
 
     The Vanguard Group was established and operates under a Funds' Service
Agreement which was approved by the shareholders of each of the Funds. The
amounts which each of the Funds has invested are adjusted from time to time in
order to maintain the proportionate relationship between each Fund's relative
net assets and its contribution to Vanguard's capital. At December 31, 1997 the
Fund had contributed capital of $425,000 to Vanguard representing 2.1% of its
capitalization. The Funds' Service Agreement provides as follows: (a) each
Vanguard Fund may invest up to .40% of its current net assets in Vanguard; and
(b) there is no other limitation on the aggregate amount that the Vanguard Funds
may contribute to Vanguard's capitalization.
 
     MANAGEMENT  Corporate management and administrative services include: (1)
executive staff; (2) accounting and financial; (3) legal and regulatory; (4)
shareholder account maintenance; (5) monitoring and control of custodian
relationships; (6) shareholder reporting; and (7) review and evaluation of
advisory and other services provided to the Funds by third parties. During the
year ended December 31, 1997 the Fund paid approximately $3,409,000 in
management and administration expenses.
 
     DISTRIBUTION  Vanguard provides all distribution and marketing activities
for the Funds in the Group. Vanguard Marketing Corporation, a wholly-owned
subsidiary of The Vanguard Group, Inc., acts as Sales Agent for the shares of
the Funds in connection with any sales made directly to investors in the states
of Florida, Missouri, New York, Ohio, Texas and such other states as it may be
required.
 
     The principal distribution expenses are for advertising, promotional
materials and marketing personnel. Distribution services may also include
organizing and offering to the public, from time to time, one or more new
investment companies which will become members of the Group. The Directors and
officers of Vanguard determine the amount to be spent annually on distribution
activities, the manner and amount to be spent on each Fund, and whether to
organize new investment companies.
 
     One half of the distribution expenses of a marketing and promotional nature
is allocated among the Funds based upon relative net assets. The remaining one
half of those expenses is allocated among the Funds based upon each Fund's sales
for the preceding 24 months relative to the total sales of the Funds as a Group,
provided, however, that no Fund's aggregate quarterly rate of contribution for
distribution expenses of a marketing and promotional nature shall exceed 125% of
average distribution expense rate for the Group, and that no Fund shall incur
annual distribution expenses in excess of 20/100 of 1% of its average month-end
net assets. During the year ended December 31, 1997 the Fund paid approximately
$1,824,000 in distribution and marketing expenses which represented 0.03% of its
average month-end net assets.
 
     INVESTMENT ADVISORY SERVICES  Vanguard also provides investment advisory
services to Vanguard Municipal Bond Fund, Vanguard Money Market Reserves,
several Portfolios of Vanguard Fixed Income Securities Fund, Vanguard California
Tax-Free Fund, Vanguard New York Tax-Free Fund, Vanguard New Jersey Tax-Free
 
                                        9
<PAGE>   101
 
Fund, Vanguard Ohio Tax-Free Fund, Vanguard Pennsylvania Tax-Free Fund, Vanguard
Florida Insured Tax-Free Fund, Vanguard Admiral Funds, Vanguard Institutional
Index Fund, Vanguard Index Trust, Vanguard International Equity Index Fund,
Vanguard Balanced Index Fund, Vanguard Tax-Managed Fund, the Aggressive Growth
Portfolio of Vanguard Horizon Fund, the REIT Index Portfolio of Vanguard
Specialized Portfolios, the Total International Portfolio of Vanguard STAR Fund,
several Portfolios of Vanguard Variable Insurance Fund, a portion of
Vanguard/Windsor II, a portion of Vanguard/Morgan Growth Fund as well as several
indexed separate accounts. These services are provided on an at-cost basis from
a money management staff employed directly by Vanguard. The compensation and
other expenses of this staff are paid by the Funds utilizing these services.
During the fiscal year ended December 31, 1997, the Fund paid approximately
$913,000 of Vanguard's expenses relating to investment advisory services.
 
DIRECTOR/TRUSTEE COMPENSATION
 
     The individuals appearing in the table below serve as Directors/Trustees of
all Vanguard Funds, and each Fund pays a proportionate share of the
Directors'/Trustees' compensation. The Funds employ their officers on a shared
basis, as well. However, officers are compensated by The Vanguard Group, Inc.,
not the Funds.
 
     INDEPENDENT DIRECTORS/TRUSTEES.  The Funds compensate their independent
Directors/Trustees -- that is, the ones who are not also officers of the
Fund -- in three ways:
 
     - The independent Directors/Trustees receive an annual fee for their
       service to the Funds, which is subject to reduction based on absences
       from scheduled Board meetings.
 
     - The independent Directors/Trustees are reimbursed for the travel and
       other expenses that they incur in attending Board meetings.
 
     - Upon retirement, the independent Directors/Trustees receive an aggregate
       annual fee of $1,000 for each year served on the Board, up to fifteen
       years of service. This annual fee is paid for ten years following
       retirement, or until the Directors'/Trustees' death.
 
     "INTERESTED" DIRECTORS/TRUSTEES.  The Funds' interested
Directors/Trustees -- Messrs. Bogle and Brennan -- receive no compensation for
their service in that capacity. However, they are paid in their role as officers
of The Vanguard Group, Inc.
 
     COMPENSATION TABLE.  The following table provides compensation details for
each of the Directors. We list the amounts paid as compensation and accrued as
retirement benefits by the Fund for each Director. In addition, the table shows
the total amount of benefits that we expect each Director/Trustee to receive
from all Vanguard Funds upon retirement, and the total amount of compensation
paid to each Director/Trustee by all Vanguard Funds. All information shown is
for the fiscal year ended December 31, 1997:
 
                            VANGUARD BOND INDEX FUND
                               COMPENSATION TABLE
 
<TABLE>
<CAPTION>
                             AGGREGATE     PENSION OR RETIREMENT      ESTIMATED        TOTAL COMPENSATION
                            COMPENSATION    BENEFITS ACCRUED AS    ANNUAL BENEFITS   FROM ALL VANGUARD FUNDS
    NAMES OF DIRECTORS       FROM FUND     PART OF FUND EXPENSES   UPON RETIREMENT    PAID TO DIRECTORS(2)
    ------------------      ------------   ---------------------   ---------------   -----------------------
<S>                         <C>            <C>                     <C>               <C>
John C. Bogle(1)                 None              None                   None                  None
John J. Brennan(1)               None              None                   None                  None
Barbara Barnes Hauptfuhrer     $1,521              $219                $15,000               $70,000
Robert E. Cawthorn             $1,521              $183                $13,000               $70,000
Bruce K. MacLaury              $1,620              $210                $12,000               $65,000
Burton G. Malkiel              $1,531              $147                $15,000               $70,000
Alfred M. Rankin, Jr.          $1,521              $115                $15,000               $70,000
John C. Sawhill                $1,521              $137                $15,000               $70,000
James O. Welch, Jr.            $1,521              $169                $15,000               $70,000
J. Lawrence Wilson             $1,521              $122                $15,000               $70,000
</TABLE>
 
(1) As "Interested Directors," Messrs. Bogle and Brennan receive no compensation
    for their service as Directors.
(2) The amounts reported in this column reflect the total compensation paid to
    each Director for their service as Director or Trustee of 35 Vanguard Funds
    (34 in the case of Mr. Malkiel; 28 in the case of Mr. MacLaury).
 
                                       10
<PAGE>   102
 
                               PORTFOLIO TRANSACTIONS
 
    HOW TRANSACTIONS ARE AFFECTED
 
     The types of securities in which the Portfolios invest are generally
purchased and sold through principal transactions, meaning that the Portfolios
normally purchase securities directly from the issuer or a primary market-maker
acting as principal for the securities on a net basis. Explicit brokerage
commissions are not paid on these transactions, although the purchase price for
securities usually includes an undisclosed compensation. Purchases from
underwriters of securities typically include a commission or concession paid by
the issuer to the underwriter, and purchases from dealers serving as market
makers typically include a dealer's mark-up (i.e., a spread between the bid and
the asked prices). During the fiscal years ended December 31, 1995, 1996 and
1997, the Portfolios did not pay any explicit brokerage commissions.
 
HOW BROKERS AND DEALERS ARE SELECTED
 
     Vanguard's Fixed Income Group chooses brokers or dealers to handle the
purchase and sale of the Portfolios' securities, and is responsible for getting
the best available price and most favorable execution for all transactions. When
the Portfolios purchase a newly issued security at a fixed price, the Group may
designate certain members of the underwriting syndicate to receive compensation
associated with that transaction. Certain dealers have agreed to rebate a
portion of such compensation directly to the Portfolios to offset their
management expenses. The Group is required to seek best execution of all
transactions and is not authorized to pay a higher brokerage commission solely
on account of the receipt of research or other services.
 
HOW THE REASONABLENESS OF BROKERAGE COMMISSIONS IS EVALUATED
 
     As previously explained, the types of securities that the Portfolios
purchase do not normally involve the payment of explicit brokerage commissions.
If any such brokerage commissions are paid, however, the Fixed Income Group will
evaluate their reasonableness by considering: (a) historical commission rates;
(b) rates which other institutional investors are paying, based upon publicly
available information; (c) rates quoted by brokers and dealers; (d) the size of
a particular transaction, in terms of the number of shares, dollar amount, and
number of clients involved; (e) the complexity of a particular transaction in
terms of both execution and settlement; (f) the level and type of business done
with a particular firm over a period of time; and (g) the extent to which the
broker or dealer has capital at risk in the transaction.
 
                              PERFORMANCE MEASURES
 
     Vanguard may use reprinted material discussing The Vanguard Group, Inc. or
any of the member funds of The Vanguard Group of Investment Companies.
 
     Each of the investment company members of The Vanguard Group, including
Vanguard Bond Index Fund, may from time to time, use one or more of the
following unmanaged indexes for comparative perfor-
mance purposes.
 
STANDARD & POOR'S 500 COMPOSITE STOCK PRICE INDEX -- is a well diversified list
of 500 companies representing the U.S. Stock Market.
 
STANDARD & POOR'S MIDCAP 400 INDEX -- is composed of 400 medium sized domestic
stocks.
 
STANDARD & POOR'S SMALLCAP 600/BARRA VALUE INDEX -- contains stocks of the S&P
SmallCap 600 Index which have a lower than average price-to-book ratio.
 
STANDARD & POOR'S SMALLCAP 600/BARRA GROWTH INDEX -- contains stocks of the S&P
SmallCap 600 Index which have a higher than average price-to-book ratio.
 
RUSSELL 1000 VALUE INDEX -- consists of the stocks in the Russell 1000 Index
(comprising the 1,000 largest U.S.-based companies measured by total market
capitalization) with the lowest price-to-book ratios, comprising 50% of the
market capitalization of the Russell 1000.
 
WILSHIRE 5000 EQUITY INDEX -- consists of more than 7,000 common equity
securities, covering all stocks in the U.S. for which daily pricing is
available.
 
                                       11
<PAGE>   103
 
WILSHIRE 4500 EQUITY INDEX -- consists of all stocks in the Wilshire 5000 except
for the 500 stocks in the Standard and Poor's 500 Index.
 
RUSSELL 3000 STOCK INDEX -- a diversified portfolio of approximately 3,000
common stocks accounting for over 90% of the market value of publicly-traded
stocks in the U.S.
 
RUSSELL 2000 STOCK INDEX -- a subset of approximately 2,000 of the smallest
stocks contained in the Russell 3000, a widely-used benchmark for small
capitalization common stocks.
 
MORGAN STANLEY CAPITAL INTERNATIONAL EAFE INDEX -- is an arithmetic, market
value-weighted average of the performance of over 900 securities listed on the
stock exchanges of countries in Europe, Australia, Asia and the Far East.
 
GOLDMAN SACHS 100 CONVERTIBLE BOND INDEX -- currently includes 71 bonds and 29
preferreds. The original list of names was generated by screening for
convertible issues of $100 million or greater in market capitalization. The
index is priced monthly.
 
SALOMON BROTHERS GNMA INDEX -- includes pools of mortgages originated by private
lenders and guaranteed by the mortgage pools of the Government National Mortgage
Association.
 
SALOMON BROTHERS HIGH-GRADE CORPORATE BOND INDEX -- consists of publicly-issued,
non-convertible corporate bonds rated Aa or Aaa. It is a value-weighted, total
return index, including approximately 800 issues with maturities of 12 years or
greater.
 
LEHMAN LONG-TERM TREASURY BOND INDEX -- is composed of all U.S. Treasury bonds
with maturities of 10 years or greater.
 
MERRILL LYNCH CORPORATE & GOVERNMENT BOND INDEX -- consists of over 4,500 U.S.
Treasury, agency and investment grade corporate bonds.
 
LEHMAN CORPORATE (BAA) BOND INDEX -- all publicly-offered fixed-rate,
nonconvertible domestic corporate bonds rated Baa by Moody's, with a maturity
longer than 1 year and with more than $25 million outstanding. This index
includes over 1,000 issues.
 
LEHMAN BROTHERS LONG-TERM CORPORATE BOND INDEX -- is a subset of the Lehman
Corporate Bond Index covering all corporate, publicly issued, fixed-rate,
nonconvertible U.S. debt issues rated at least Baa, with at least $50 million
principal outstanding and maturity greater than 10 years.
 
BOND BUYER MUNICIPAL BOND INDEX -- is a yield index on current coupon high-grade
general obligation municipal bonds.
 
STANDARD & POOR'S PREFERRED INDEX -- is a yield index based upon the average
yield for four high-grade, non-callable preferred stock issues.
 
NASDAQ INDUSTRIAL INDEX -- is composed of more than 3,000 industrial issues. It
is a value-weighted index calculated on price change only and does not include
income.
 
COMPOSITE INDEX -- 70% Standard & Poor's 500 Index and 30% NASDAQ Industrial
Index.
 
COMPOSITE INDEX -- 65% Standard & Poor's 500 Index and 35% Lehman Long-Term
Corporate AA or Better Bond Index.
 
COMPOSITE INDEX -- 65% Lehman Long-Term Corporate AA or Better Bond Index and a
35% weighting in a blended equity composite (75% Standard & Poor's/BARRA Value
Index, 12.5% Standard & Poor's Utilities Index and 12.5% Standard & Poor's
Telephone Index).
 
LEHMAN LONG-TERM CORPORATE AA OR BETTER BOND INDEX -- consists of all publicly
issued, fixed rate, nonconvertible investment grade, dollar-denominated,
SEC-registered corporate debt rated AA or AAA.
 
LEHMAN BROTHERS AGGREGATE BOND INDEX -- is a market-weighted index that contains
individually priced U.S. Treasury, agency, corporate, and mortgage pass-through
securities corporate rated BBB- or better. The Index has a market value of over
$4 trillion.
 
LEHMAN BROTHERS MUTUAL FUND SHORT (1-5) GOVERNMENT/CORPORATE INDEX -- is a
market-weighted index that contains individually priced U.S. Treasury, agency,
and corporate investment grade bonds rated BBB- or better with maturities
between 1 and 5 years. The index has a market value of over $1.6 trillion.
 
                                       12
<PAGE>   104
 
LEHMAN BROTHERS MUTUAL FUND INTERMEDIATE (5-10) GOVERNMENT/CORPORATE INDEX -- is
a market-weighted index that contains individually priced U.S. Treasury, agency,
and corporate securities rated BBB- or better with maturities between 5 and 10
years. The index has a market value of over $700 billion.
 
LEHMAN BROTHERS LONG (10+) GOVERNMENT/CORPORATE INDEX -- is a market-weighted
index that contains individually priced U.S. Treasury, agency, and corporate
securities rated BBB- or better with maturities greater than 10 years. The index
has a market value of over $900 billion.
 
LIPPER SMALL COMPANY GROWTH FUND AVERAGE -- the average performance of small
company growth funds as defined by Lipper Analytical Services, Inc. Lipper
defines a small company growth fund as a fund that by prospectus or portfolio
practice, limits its investments to companies on the basis of the size of the
company. From time to time, Vanguard may advertise using the average performance
and/or the average expense ratio of the small company growth funds. (This fund
category was first established in 1982. For years prior to 1982, the results of
the Lipper Small Company Growth category were estimated using the returns of the
Funds that constituted the Group at its inception.)
 
LIPPER BALANCED FUND AVERAGE -- an industry benchmark of average balanced funds
with similar investment objectives and policies, as measured by Lipper
Analytical Services, Inc.
 
LIPPER NON-GOVERNMENT MONEY MARKET FUND AVERAGE -- an industry benchmark of
average non-government money market funds with similar investment objectives and
policies, as measured by Lipper Analytical Services, Inc.
 
LIPPER GOVERNMENT MONEY MARKET FUND AVERAGE -- an industry benchmark of average
government money market funds with similar investment objectives and policies,
as measured by Lipper Analytical Services, Inc.
 
LIPPER GENERAL EQUITY FUND AVERAGE -- an industry benchmark of average general
equity funds with similar investment objectives and policies, as measured by
Lipper Analytical Services, Inc.
 
LIPPER FIXED INCOME FUND AVERAGE -- an industry benchmark of average fixed
income funds with similar investment objectives and policies, as measured by
Lipper Analytical Services, Inc.
 
                              FINANCIAL STATEMENTS
 
     The Fund's financial statements as of and for the year ended December 31,
1997, appearing in the Fund's 1997 Annual Report to Shareholders, and the report
thereon of Price Waterhouse LLP, independent accountants, also appearing
therein, are incorporated by reference in this Statement of Additional
Information.
 
                    APPENDIX -- DESCRIPTION OF BOND RATINGS
 
     The Fund will invest primarily in investment grade bonds (i.e., those rated
at least Baa3 by Moody's Investors Service, Inc. or those rated BBB- by Standard
& Poor's Corporation.) In the event that a Bond held by the Fund is downgraded,
the adviser, may continue to hold such bond. Excerpts from Moody's Investors
Service, Inc. description of its four highest bond ratings:
 
     AAA -- judged to be the best quality by all standards. Together with the Aa
group they comprise what are generally known as high grade bonds; A -- possess
many favorable investment attributes and are to be considered as "upper medium
grade obligations"; BAA -- considered as medium grade obligations (i.e., they
are neither highly protected nor poorly secured). Interest payments and
principal security appear adequate for the present but certain protective
elements may be lacking or may be characteristically unreliable over any great
length of time. Such bonds lack outstanding investment characteristics and in
fact have speculative characteristics as well.
 
     Moody's also supplies numerical indicators 1, 2 and 3 to rating categories.
The modifier 1 indicates that the obligation ranks in the higher end of its
generic rating category; the modifier 2 indicates a mid-range ranking; and 3
indicates a ranking toward the lower end of that generic rating category.
 
                                       13
<PAGE>   105
 
     Excerpts from Standard & Poor's Corporation description of its four highest
bond ratings:
 
     AAA -- highest rating assigned by S&P. Capacity to pay interest and repay
principal is extremely strong; AA -- also qualify as investment grade
obligations, a very strong capacity to pay interest and repay principal and
differs from AAA -- issues only in small degree; A -- regarded as upper medium
grade. It has a strong capacity to pay interest and repay principal although it
is somewhat susceptible to the adverse effects of changes in circumstances and
economic conditions than debt in higher rated categories; BBB -- regarded as
having an adequate capacity to pay interest and repay principal. Whereas it
normally exhibits adequate protection parameters, adverse economic conditions or
changing circumstances are more likely to lead to a weakened capacity to pay
interest and repay principal for debt in this category than in higher rated
categories.
 
     Standard & Poor's applies indicators "+", no character and "-" to its
rating categories. The indicators show relative standing within the major rating
categories.
 
                                       14


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