MORGAN STANLEY DEAN WITTER HIGH YIELD SECURITIES INC
497, 1998-11-12
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<PAGE>
                         MORGAN STANLEY DEAN WITTER
                         HIGH YIELD SECURITIES INC.
                         PROSPECTUS--OCTOBER 29, 1998
 
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MORGAN STANLEY DEAN WITTER HIGH YIELD SECURITIES INC. (THE "FUND") IS AN
OPEN-END DIVERSIFIED MANAGEMENT INVESTMENT COMPANY WHOSE PRIMARY INVESTMENT
OBJECTIVE IS TO EARN A HIGH LEVEL OF CURRENT INCOME. AS A SECONDARY OBJECTIVE,
THE FUND WILL SEEK CAPITAL APPRECIATION, BUT ONLY WHEN CONSISTENT WITH ITS
PRIMARY OBJECTIVE. THE FUND SEEKS HIGH CURRENT INCOME BY INVESTING PRINCIPALLY
IN FIXED-INCOME SECURITIES WHICH ARE RATED IN THE LOWER CATEGORIES BY
ESTABLISHED RATING SERVICES (BAA OR LOWER BY MOODY'S INVESTORS SERVICE, INC. OR
BBB OR LOWER BY STANDARD & POOR'S CORPORATION) OR ARE NON-RATED SECURITIES OF
COMPARABLE QUALITY.
 
INVESTORS SHOULD CAREFULLY CONSIDER THE RELATIVE RISKS, INCLUDING THE RISK OF
DEFAULT, OF INVESTING IN HIGH YIELD SECURITIES, WHICH ARE COMMONLY KNOWN AS JUNK
BONDS. BONDS OF THIS TYPE ARE CONSIDERED TO BE SPECULATIVE WITH REGARD TO THE
PAYMENT OF INTEREST AND RETURN OF PRINCIPAL. INVESTORS SHOULD ALSO BE COGNIZANT
OF THE FACT THAT SUCH SECURITIES ARE NOT GENERALLY MEANT FOR SHORT-TERM
INVESTING AND SHOULD ASSESS THE RISKS ASSOCIATED WITH AN INVESTMENT IN THE FUND.
(See "Investment Objectives and Policies.")
 
The Fund offers four classes of shares (each, a "Class"), each with a different
combination of sales charges, ongoing fees and other features. The different
distribution arrangements permit an investor to choose the method of purchasing
shares that the investor believes is most beneficial given the amount of the
purchase, the length of time the investor expects to hold the shares and other
relevant circumstances. (See "Purchase of Fund Shares--Alternative Purchase
Arrangements.")
 
<TABLE>
<CAPTION>
TABLE OF CONTENTS
 
<S>                                                 <C>
Prospectus Summary................................       2
 
Summary of Fund Expenses..........................       4
 
Financial Highlights..............................       5
 
The Fund and its Management.......................       8
 
Investment Objectives and Policies................       8
 
 Special Risk Considerations......................       9
 
Investment Restrictions...........................      13
 
Purchase of Fund Shares...........................      13
 
Shareholder Services..............................      21
 
Redemptions and Repurchases.......................      24
 
Dividends, Distributions and Taxes................      25
 
Performance Information...........................      26
 
Additional Information............................      26
 
Appendix..........................................      27
</TABLE>
 
This Prospectus sets forth concisely the information you should know before
investing in the Fund. It should be read and retained for future reference.
Additional information about the Fund is contained in the Statement of
Additional Information, dated October 29, 1998, which has been filed with the
Securities and Exchange Commission, and which is available at no charge upon
request of the Fund at the address or telephone numbers listed on this page. The
Statement of Additional Information is incorporated herein by reference.
 
SHARES OF THE FUND ARE NOT DEPOSITS OR OBLIGATIONS OF, OR GUARANTEED OR ENDORSED
BY, ANY BANK, AND THE SHARES ARE NOT FEDERALLY INSURED BY THE FEDERAL DEPOSIT
INSURANCE CORPORATION, THE FEDERAL RESERVE BOARD, OR ANY OTHER AGENCY.
 
MORGAN STANLEY DEAN WITTER
HIGH YIELD SECURITIES INC.
TWO WORLD TRADE CENTER
NEW YORK, NEW YORK 10048
(212) 392-2550 or (800) 869-NEWS (toll-free)
 
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  THESE SECURITIES HAVE NOT BEEN APPROVED OR DISAPPROVED BY THE SECURITIES AND
EXCHANGE COMMISSION OR ANY STATE SECURITIES COMMISSION NOR HAS THE COMMISSION OR
  ANY STATE SECURITIES COMMISSION PASSED UPON THE ACCURACY OR ADEQUACY OF THIS
     PROSPECTUS. ANY REPRESENTATION TO THE CONTRARY IS A CRIMINAL OFFENSE.
 
           MORGAN STANLEY DEAN WITTER DISTRIBUTORS INC., DISTRIBUTOR
<PAGE>
PROSPECTUS SUMMARY
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<TABLE>
<S>             <C>
THE FUND        An open-end diversified management investment company investing principally in
                lower-rated fixed- income securities (see page 8).
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SHARES OFFERED  Common stock of $0.01 par value (see page 26). The Fund offers four Classes of shares,
                each with a different combination of sales charges, ongoing fees and other features (see
                pages 13-21).
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MINIMUM         The minimum initial investment for each Class is $1,000 ($100 if the account is opened
PURCHASE        through EasyInvest-SM-). Class D shares are only available to persons investing $5
                million ($25 million for certain qualified plans) or more and to certain other limited
                categories of investors. For the purpose of meeting the minimum $5 million (or $25
                million) investment for Class D shares, and subject to the $1,000 minimum initial
                investment for each Class of the Fund, an investor's existing holdings of Class A shares
                and shares of funds for which Morgan Stanley Dean Witter Advisors Inc. serves as
                investment manager ("Morgan Stanley Dean Witter Funds") that are sold with a front-end
                sales charge, and concurrent investments in Class D shares of the Fund and other Morgan
                Stanley Dean Witter Funds that are multiple class funds, will be aggregated. The minimum
                subsequent investment is $100 (see page 14).
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INVESTMENT      A high level of current income primarily; capital appreciation is secondary (see page
OBJECTIVES      8).
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INVESTMENT      High yield fixed-income securities, principally rated Baa/BBB or lower, and non-rated
POLICIES        securities of comparable quality. However, the Fund may also invest in municipal
                securities, futures
                and options and common stock (see pages 8-13).
- -------------------------------------------------------------------------------------------------------
INVESTMENT      Morgan Stanley Dean Witter Advisors Inc., the Investment Manager of the Fund, and its
MANAGER         wholly-owned subsidiary, Morgan Stanley Dean Witter Services Company, Inc., serve in
                various investment management, advisory, management and administrative capacities to 100
                investment companies and other portfolios, with assets of approximately $113.6 billion
                at September 30, 1998 (see page 8).
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MANAGEMENT FEE  The monthly fee is at an annual rate of 1/2 of 1% of average daily net assets, scaled
                down on assets over $500 million (see page 8).
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DISTRIBUTOR     Morgan Stanley Dean Witter Distributors Inc. (the "Distributor") is the Distributor of
AND             the Fund's shares. The Fund has adopted a distribution plan pursuant to Rule 12b-1 under
DISTRIBUTION    the Investment Company Act (the "12b-1 Plan") with respect to the distribution fees paid
FEE             by the Class A, Class B and Class C shares of the Fund to the Distributor. The entire
                12b-1 fee payable by Class A and a portion of the 12b-1 fee payable by each of Class B
                and Class C equal to 0.20% of the average daily net assets of Class B and 0.25% of the
                average daily net assets of Class C are currently each characterized as a service fee
                within the meaning of the National Association of Securities Dealers, Inc. guidelines.
                The remaining portion of the 12b-1 fee, if any, is characterized as an asset-based sales
                charge (see pages 13 and 20).
- -------------------------------------------------------------------------------------------------------
ALTERNATIVE     Four classes of shares are offered:
PURCHASE
ARRANGEMENTS    - Class A shares are offered with a front-end sales charge, starting at 4.25% and
                reduced for larger purchases. Investments of $1 million or more (and investments by
                certain other limited categories of investors) are not subject to any sales charge at
                the time of purchase but a contingent deferred sales charge ("CDSC") of 1.0% may be
                imposed on redemptions within one year of purchase. The Fund is authorized to reimburse
                the Distributor for specific expenses incurred in promoting the distribution of the
                Fund's Class A shares and servicing shareholder accounts pursuant to the Fund's 12b-1
                Plan. Reimbursement may in no event exceed an amount equal to payments at an annual rate
                of 0.25% of average daily net assets of the Class (see pages 13, 16 and 20).
                - Class B shares are offered without a front-end sales charge, but will in most cases be
                subject to a CDSC (scaled down from 5.0% to 1.0%) if redeemed within six years after
                purchase. The CDSC will be imposed on any redemption of shares if after such redemption
                the aggregate current value of a Class B account with the Fund falls below the aggregate
                amount of the investor's purchase payments made during the six years preceding the
                redemption. A different CDSC schedule applies to investments by certain qualified plans.
                Class B shares are also subject to a 12b-1 fee assessed at the annual rate of 0.75% of
                the average daily net assets of Class B. Class B shares convert to Class A shares
                approximately ten years after the date of the original purchase (see pages 13, 17 and
                20).
                - Class C shares are offered without a front-end sales charge, but will in most cases be
                subject to a CDSC of 1.0% if redeemed within one year after purchase. The Fund is
                authorized to reimburse the Distributor for specific expenses incurred in promoting the
                distribution of the Fund's Class C shares and servicing shareholder accounts pursuant to
                the Fund's 12b-1 Plan. Reimbursement may in no event exceed an amount equal to payments
                at an annual rate of 0.85% of average daily net assets of the Class (see pages 13, 19
                and 20).
</TABLE>
 
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2
<PAGE>
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<TABLE>
<S>             <C>
                - Class D shares are offered only to investors meeting an initial investment minimum of
                $5 million ($25 million for certain qualified plans) and to certain other limited
                categories of investors. Class D shares are offered without a front-end sales charge or
                CDSC and are not subject to any 12b-1 fee (see pages 16, 24 and 25). All shares of the
                Fund held prior to July 28, 1997 have been designated Class D shares. Additional
                investments in Class D shares by shareholders holding such shares may only be made if
                those shareholders are otherwise eligible to purchase Class D shares. However,
                shareholders holding such shares will receive the benefit of the value of such shares
                towards reduced sales charges on purchases of Class A shares pursuant to the Fund's
                "Right of Accumulation" (see pages 13, 19 and 20).
- -------------------------------------------------------------------------------------------------------
DIVIDENDS AND   Dividends from net investment income are declared and paid monthly; distributions from
CAPITAL GAINS   net capital gains, if any, are paid at least annually. The Fund may, however, determine
DISTRIBUTIONS   to retain all or part of any net mid-term and net long-term capital gains in any year
                for reinvestment. Dividends and capital gains distributions paid on shares of a Class
                are automatically reinvested in additional shares of the same Class at net asset value
                unless the shareholder elects to receive cash. Shares acquired by dividend and
                distribution reinvestment will not be subject to any sales charge or CDSC (see pages 21
                and 25).
- -------------------------------------------------------------------------------------------------------
REDEMPTION      Shares are redeemable by the shareholder at net asset value less any applicable CDSC on
                Class A, Class B or Class C shares. An account may be involuntarily redeemed if the
                total value of the account is less than $100 or, if the account was opened through
                EasyInvest-SM-, if after twelve months the shareholder has invested less than $1,000 in
                the account (see page 24).
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RISKS           The net asset value of the Fund's shares will fluctuate with changes in the market value
                of its portfolio securities. The Fund's yield will also vary based on the yield of the
                Fund's portfolio securities. Compared with higher rated, lower yielding fixed-income
                securities, portfolio securities of the Fund may be subject to greater risk of loss of
                income and principal, including the risk of default, and greater risk of increases and
                decreases in net asset value due to market fluctuations. The Fund may purchase foreign
                securities, when-issued and delayed delivery and when, as and if issued securities and
                other securities subject to repurchase agreements which involve certain special risks.
                The Fund may purchase common stock which is exchangeable for fixed-income securities in
                circumstances involving takeovers or recapitalizations. The Fund may also invest in
                futures and options which may be considered speculative in nature and may involve
                greater risks than those customarily assumed by certain other investment companies which
                do not invest in such instruments. Investors should review the investment objectives and
                policies of the Fund carefully and consider their ability to assume the risks involved
                in purchasing shares of the Fund (see pages 9-12).
</TABLE>
 
- --------------------------------------------------------------------------------
 
  THE ABOVE IS QUALIFIED IN ITS ENTIRETY BY THE DETAILED INFORMATION APPEARING
              ELSEWHERE IN THIS PROSPECTUS AND IN THE STATEMENT OF
                            ADDITIONAL INFORMATION.
 
                                                                               3
<PAGE>
SUMMARY OF FUND EXPENSES
- --------------------------------------------------------------------------------
 
The following table illustrates all expenses and fees that a shareholder of the
Fund will incur. The expenses and fees set forth in the table are based on the
expenses and fees for the fiscal year ended August 31, 1998.
 
<TABLE>
<CAPTION>
                                                                                   CLASS A    CLASS B    CLASS C    CLASS D
                                                                                  ---------   -------   ---------   -------
<S>                                                                               <C>         <C>       <C>         <C>
SHAREHOLDER TRANSACTION EXPENSES
Maximum Sales Charge Imposed on Purchases (as a percentage of offering price)...   4.25%(1)    None      None        None
Sales Charge Imposed on Dividend Reinvestments..................................   None        None      None        None
Maximum Contingent Deferred Sales Charge (as a percentage of original purchase
 price or redemption proceeds)..................................................   None(2)    5.00%(3)   1.00%(4)    None
Redemption Fees.................................................................   None        None      None        None
Exchange Fee....................................................................   None        None      None        None
 
ANNUAL FUND OPERATING EXPENSES (AS A PERCENTAGE OF AVERAGE NET ASSETS)
Management Fees (5).............................................................      0.40%     0.40%       0.40%     0.40%
12b-1 Fees (6) (7)..............................................................      0.24%     0.74%       0.85%    None
Other Expenses (5)..............................................................      0.11%     0.11%       0.11%     0.11%
Total Fund Operating Expenses...................................................      0.75%     1.25%       1.36%     0.51%
</TABLE>
 
- ---------------
(1) REDUCED FOR PURCHASES OF $25,000 AND OVER (SEE "PURCHASE OF FUND
    SHARES--INITIAL SALES CHARGE ALTERNATIVE--CLASS A SHARES").
(2) INVESTMENTS THAT ARE NOT SUBJECT TO ANY SALES CHARGE AT THE TIME OF PURCHASE
    ARE SUBJECT TO A CDSC OF 1.00% THAT WILL BE IMPOSED ON REDEMPTIONS MADE
    WITHIN ONE YEAR AFTER PURCHASE, EXCEPT FOR CERTAIN SPECIFIC CIRCUMSTANCES
    (SEE "PURCHASE OF FUND SHARES--INITIAL SALES CHARGE ALTERNATIVE--CLASS A
    SHARES").
(3) THE CDSC IS SCALED DOWN TO 1.00% DURING THE SIXTH YEAR, REACHING ZERO
    THEREAFTER.
(4) ONLY APPLICABLE TO REDEMPTIONS MADE WITHIN ONE YEAR AFTER PURCHASE (SEE
    "PURCHASE OF FUND SHARES-- LEVEL LOAD ALTERNATIVE--CLASS C SHARES").
(5) MANAGEMENT FEES AND OTHER EXPENSES ARE BASED ON THE FUND'S ACTUAL AGGREGATE
    EXPENSES.
(6) THE 12b-1 FEE IS ACCRUED DAILY AND PAYABLE MONTHLY. THE ENTIRE 12b-1 FEE
    PAYABLE BY CLASS A AND A PORTION OF THE 12b-1 FEE PAYABLE BY EACH OF CLASS B
    AND CLASS C EQUAL TO 0.20% OF THE AVERAGE DAILY NET ASSETS OF CLASS B AND
    0.25% OF THE AVERAGE DAILY NET ASSETS OF CLASS C ARE CURRENTLY EACH
    CHARACTERIZED AS A SERVICE FEE WITHIN THE MEANING OF NATIONAL ASSOCIATION OF
    SECURITIES DEALERS, INC. ("NASD") GUIDELINES AND ARE PAYMENTS MADE FOR
    PERSONAL SERVICE AND/OR MAINTENANCE OF SHAREHOLDER ACCOUNTS. THE REMAINDER
    OF THE 12b-1 FEE, IF ANY, IS AN ASSET-BASED SALES CHARGE, AND IS A
    DISTRIBUTION FEE PAID TO THE DISTRIBUTOR TO COMPENSATE IT FOR THE SERVICES
    PROVIDED AND THE EXPENSES BORNE BY THE DISTRIBUTOR AND OTHERS IN THE
    DISTRIBUTION OF THE FUND'S SHARES (SEE "PURCHASE OF FUND SHARES--PLAN OF
    DISTRIBUTION").
(7) UPON CONVERSION OF CLASS B SHARES TO CLASS A SHARES, SUCH SHARES WILL BE
    SUBJECT TO THE LOWER 12b-1 FEE APPLICABLE TO CLASS A SHARES. NO SALES CHARGE
    IS IMPOSED AT THE TIME OF CONVERSION OF CLASS B SHARES TO CLASS A SHARES.
    CLASS C SHARES DO NOT HAVE A CONVERSION FEATURE AND, THEREFORE, ARE SUBJECT
    TO AN ONGOING 0.85% DISTRIBUTION FEE (SEE "PURCHASE OF FUND
    SHARES--ALTERNATIVE PURCHASE ARRANGEMENTS").
 
<TABLE>
<CAPTION>
EXAMPLES                                            1 YEAR    3 YEARS   5 YEARS   10 YEARS
                                                    -------   -------   -------   --------
<S>                                                 <C>       <C>       <C>       <C>
You would pay the following expenses on a $1,000
 investment assuming (1) a 5% annual return and
 (2) redemption at the end of each time period:
    Class A.......................................    $50       $65       $82       $131
    Class B.......................................    $63       $70       $88       $151
    Class C.......................................    $24       $43       $74       $163
    Class D.......................................    $ 5       $16       $28       $ 64
You would pay the following expenses on the same
 $1,000 investment assuming no redemption at the
 end of the period:
    Class A.......................................    $50       $65       $82       $131
    Class B.......................................    $13       $40       $68       $151
    Class C.......................................    $14       $43       $74       $163
    Class D.......................................    $ 5       $16       $28       $ 64
</TABLE>
 
THE ABOVE EXAMPLES SHOULD NOT BE CONSIDERED A REPRESENTATION OF PAST OR FUTURE
EXPENSES OR PERFORMANCE. ACTUAL EXPENSES OF EACH CLASS MAY BE GREATER OR LESS
THAN THOSE SHOWN.
 
The purpose of this table is to assist the investor in understanding the various
costs and expenses that an investor in the Fund will bear directly or
indirectly. For a more complete description of these costs and expenses, see
"The Fund and its Management," "Purchase of Fund Shares--Plan of Distribution"
and "Redemptions and Repurchases."
 
Long-term shareholders of Class B and Class C may pay more in sales charges,
including distribution fees, than the economic equivalent of the maximum
front-end sales charges permitted by the NASD.
 
4
<PAGE>
FINANCIAL HIGHLIGHTS
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The following ratios and per share data for a share of capital stock outstanding
throughout each period have been audited by PricewaterhouseCoopers LLP,
independent accountants. The financial highlights should be read in conjunction
with the financial statements, the notes thereto and the unqualified report of
independent accountants which are contained in the Statement of Additional
Information. Further information about the performance of the Fund is contained
in the Fund's Annual Report to Stockholders, which may be obtained without
charge upon request to the Fund.
 
<TABLE>
<CAPTION>
                                                                FOR THE YEAR ENDED AUGUST 31,
                                ---------------------------------------------------------------------------------------------
CLASS D SHARES                  1998++        1997*    1996     1995     1994     1993     1992     1991     1990      1989
                                -------      -------  -------  -------  -------  -------  -------  -------  -------   -------
 
<S>                             <C>          <C>      <C>      <C>      <C>      <C>      <C>      <C>      <C>       <C>
PER SHARE OPERATING
 PERFORMANCE:
Net asset value, beginning of
 period.......................  $  6.82      $  6.71  $  6.77  $  6.83  $  7.58  $  7.23  $  5.92  $  6.78  $ 10.40   $ 11.99
                                -------      -------  -------  -------  -------  -------  -------  -------  -------   -------
Net investment income.........     0.78         0.79     0.83     0.80     0.79     0.89     0.95     0.94     1.48      1.67
Net realized and unrealized
 gain (loss)..................    (0.71)        0.15    (0.12)   (0.06)   (0.68)    0.54     1.04    (0.86)   (3.78)    (1.48)
                                -------      -------  -------  -------  -------  -------  -------  -------  -------   -------
Total from investment
 operations...................     0.07         0.94     0.71     0.74     0.11     1.43     1.99     0.08    (2.30)     0.19
                                -------      -------  -------  -------  -------  -------  -------  -------  -------   -------
Less dividends and
 distributions from:
  Net investment income.......    (0.73)       (0.83)   (0.77)   (0.80)   (0.86)   (1.08)   (0.68)   (0.94)   (1.32)    (1.75)
  Paid-in-capital.............    --           --       --       --       --       --       --       --       --        (0.03)
                                -------      -------  -------  -------  -------  -------  -------  -------  -------   -------
Total dividends and
 distributions................    (0.73)       (0.83)   (0.77)   (0.80)   (0.86)   (1.08)   (0.68)   (0.94)   (1.32)    (1.78)
                                -------      -------  -------  -------  -------  -------  -------  -------  -------   -------
Net asset value, end of
 period.......................  $  6.16      $  6.82  $  6.71  $  6.77  $  6.83  $  7.58  $  7.23  $  5.92  $  6.78   $ 10.40
                                -------      -------  -------  -------  -------  -------  -------  -------  -------   -------
                                -------      -------  -------  -------  -------  -------  -------  -------  -------   -------
 
TOTAL INVESTMENT RETURN+......     0.63%       15.01%   11.07%   11.98%    0.93%   22.29%   35.46%    4.67%  (23.28)%    1.39%
 
RATIOS TO AVERAGE NET ASSETS:
Expenses......................     0.51%(1)     0.68%    0.66%    0.79%    0.69%    0.67%    0.77%    0.87%    0.60%     0.49%
Net investment income.........    11.54%(1)    11.78%   12.27%   12.06%   10.40%   12.14%   13.96%   16.47%   17.67%    14.61%
 
SUPPLEMENTAL DATA:
Net assets, end of period, in
 millions.....................     $401         $479     $460     $455     $478     $540     $512     $436     $690    $1,794
Portfolio turnover rate.......       66%         113%      49%      74%     127%     173%     113%      93%      21%       55%
</TABLE>
 
- -------------
 * PRIOR TO JULY 28, 1997, THE FUND ISSUED ONE CLASS OF SHARES. ALL SHARES OF
   THE FUND HELD PRIOR TO THAT DATE HAVE BEEN DESIGNATED CLASS D SHARES.
 ++ THE PER SHARE AMOUNTS WERE COMPUTED USING AN AVERAGE NUMBER OF SHARES
    OUTSTANDING DURING THE PERIOD.
 + CALCULATED BASED ON THE NET ASSET VALUE AS OF THE LAST BUSINESS DAY OF THE
   PERIOD.
(1) REFLECTS OVERALL FUND RATIOS FOR INVESTMENT INCOME AND NON-CLASS SPECIFIC
    EXPENSES.
 
                                                                               5
<PAGE>
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<TABLE>
<CAPTION>
                                                                                            FOR THE PERIOD
                                                                          FOR THE YEAR      JULY 28, 1997*
                                                                             ENDED             THROUGH
                                                                           AUGUST 31,         AUGUST 31,
CLASS A SHARES                                                               1998++             1997++
                                                                        ----------------   ----------------
<S>                                                                     <C>                <C>
PER SHARE OPERATING PERFORMANCE:
Net asset value, beginning of period..................................      $  6.82            $  6.83
                                                                             ------             ------
Net investment income.................................................         0.76               0.07
Net realized and unrealized loss......................................        (0.71)             (0.03)
                                                                             ------             ------
Total from investment operations......................................         0.05               0.04
                                                                             ------             ------
Less dividends from net investment income.............................        (0.71)             (0.05)
                                                                             ------             ------
Net asset value, end of period........................................      $  6.16            $  6.82
                                                                             ------             ------
                                                                             ------             ------
TOTAL INVESTMENT RETURN+..............................................         0.40%              0.65%(1)
RATIOS TO AVERAGE NET ASSETS:
Expenses..............................................................         0.75%(3)           0.93%(2)
Net investment income.................................................        11.30%(3)          11.80%(2)
SUPPLEMENTAL DATA:
Net assets, end of period, in thousands...............................      $30,678             $1,996
Portfolio turnover rate...............................................           66%               113%
 
CLASS B SHARES
PER SHARE OPERATING PERFORMANCE:
Net asset value, beginning of period..................................      $  6.82            $  6.83
                                                                             ------             ------
Net investment income.................................................         0.73               0.07
Net realized and unrealized loss......................................        (0.72)             (0.03)
                                                                             ------             ------
Total from investment operations......................................         0.01               0.04
                                                                             ------             ------
Less dividends from net investment income.............................        (0.68)             (0.05)
                                                                             ------             ------
Net asset value, end of period........................................      $  6.15            $  6.82
                                                                             ------             ------
                                                                             ------             ------
TOTAL INVESTMENT RETURN+..............................................        (0.23)%             0.62%(1)
RATIOS TO AVERAGE NET ASSETS:
Expenses..............................................................         1.25%(3)           1.42%(2)
Net investment income.................................................        10.80%(3)          11.28%(2)
SUPPLEMENTAL DATA:
Net assets, end of period, in thousands...............................   $1,761,147            $15,828
Portfolio turnover rate...............................................           66%               113%
</TABLE>
 
- -------------
 * THE DATE SHARES WERE FIRST ISSUED.
 ++ THE PER SHARE AMOUNTS WERE COMPUTED USING AN AVERAGE NUMBER OF SHARES
    OUTSTANDING DURING THE PERIOD.
 + DOES NOT REFLECT THE DEDUCTION OF SALES CHARGE. CALCULATED BASED ON THE NET
   ASSET VALUE AS OF THE LAST BUSINESS DAY OF THE PERIOD.
(1) NOT ANNUALIZED.
(2) ANNUALIZED.
(3) REFLECTS OVERALL FUND RATIOS FOR INVESTMENT INCOME AND NON-CLASS SPECIFIC
    EXPENSES.
 
6
<PAGE>
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<TABLE>
<CAPTION>
                                                                                            FOR THE PERIOD
                                                                          FOR THE YEAR      JULY 28, 1997*
                                                                             ENDED             THROUGH
                                                                           AUGUST 31,         AUGUST 31,
CLASS C SHARES                                                               1998++             1998++
                                                                        ----------------   ----------------
<S>                                                                     <C>                <C>
PER SHARE OPERATING PERFORMANCE:
Net asset value, beginning of period..................................      $  6.82            $  6.83
                                                                             ------             ------
Net investment income.................................................         0.72               0.07
Net realized and unrealized loss......................................        (0.72)             (0.03)
                                                                             ------             ------
Total from investment operations......................................         0.00               0.04
                                                                             ------             ------
Less dividends from net investment income.............................        (0.67)             (0.05)
                                                                             ------             ------
Net asset value, end of period........................................      $  6.15            $  6.82
                                                                             ------             ------
                                                                             ------             ------
TOTAL INVESTMENT RETURN+..............................................        (0.34)%             0.62%(1)
RATIOS TO AVERAGE NET ASSETS:
Expenses..............................................................         1.36%(3)           1.52%(2)
Net investment income.................................................        10.69%(3)          11.18%(2)
SUPPLEMENTAL DATA:
Net assets, end of period, in thousands...............................      $56,626             $5,225
Portfolio turnover rate...............................................           66%               113%
</TABLE>
 
- -------------
 * THE DATE SHARES WERE FIRST ISSUED.
 ++ THE PER SHARE AMOUNTS WERE COMPUTED USING AN AVERAGE NUMBER OF SHARES
    OUTSTANDING DURING THE PERIOD.
 + DOES NOT REFLECT THE DEDUCTION OF SALES CHARGE. CALCULATED BASED ON THE NET
   ASSET VALUE AS OF THE LAST BUSINESS DAY OF THE PERIOD.
(1) NOT ANNUALIZED.
(2) ANNUALIZED.
(3) REFLECTS OVERALL FUND RATIOS FOR INVESTMENT INCOME AND NON-CLASS SPECIFIC
    EXPENSES.
 
                                                                               7
<PAGE>
THE FUND AND ITS MANAGEMENT
- --------------------------------------------------------------------------------
 
Morgan Stanley Dean Witter High Yield Securities Inc. (the "Fund") (formerly
named Dean Witter High Yield Securities Inc.) is an open-end diversified
management investment company incorporated in Maryland on June 14, 1979.
 
    Morgan Stanley Dean Witter Advisors Inc. ("MSDW Advisors" or the "Investment
Manager"), whose address is Two World Trade Center, New York, New York 10048, is
the Fund's Investment Manager. The Investment Manager is a wholly-owned
subsidiary of Morgan Stanley Dean Witter & Co., a preeminent global financial
services firm that maintains leading market positions in each of its three
primary businesses--securities, asset management and credit services. The
Investment Manager, which was incorporated in July, 1992 under the name Dean
Witter InterCapital Inc., changed its name to Morgan Stanley Dean Witter
Advisors Inc. on June 22, 1998.
 
    MSDW Advisors and its wholly-owned subsidiary, Morgan Stanley Dean Witter
Services Company Inc. ("MSDW Services"), serve in various investment management,
advisory, management and administrative capacities to 100 investment companies,
28 of which are listed on the New York Stock Exchange, with combined total
assets of approximately $109.5 billion as of September 30, 1998. The Investment
Manager also manages, and advises managers of, common stock portfolios of
pension plans, other institutions and individuals which aggregated approximately
$4.1 billion at such date.
 
    The Fund has retained the Investment Manager to provide administrative
services, manage its business affairs and manage the investment of the Fund's
assets, including the placing of orders for the purchase and sale of portfolio
securities. MSDW Advisors has retained MSDW Services to perform the
aforementioned administrative services for the Fund.
 
    The Fund's Board of Directors reviews the various services provided by or
under the direction of the Investment Manager to ensure that the Fund's general
investment policies and programs are being properly carried out and that
administrative services are being provided to the Fund in a satisfactory manner.
 
    As full compensation for the services and facilities furnished to the Fund
and expenses of the Fund assumed by the Investment Manager, the Fund pays the
Investment Manager monthly compensation calculated daily by applying a
percentage rate to the daily net assets of the Fund which declines as net assets
of the Fund reach levels over $500 million (up to $3 billion). For the fiscal
year ended August 31, 1998, the Fund accrued total compensation to the
Investment Manager amounting to 0.40% of the Fund's average daily net assets and
the total expenses of each Class amounted to 0.75%, 1.25%, 1.36% and 0.51% of
the average daily net assets of Class A, Class B, Class C and Class D,
respectively.
 
INVESTMENT OBJECTIVES AND POLICIES
- --------------------------------------------------------------------------------
 
The primary investment objective of the Fund is to earn a high level of current
income. As a secondary objective, the Fund will seek capital appreciation, but
only when consistent with its primary objective. Capital appreciation may
result, for example, from an improvement in the credit standing of an issuer
whose securities are held in the Fund's portfolio or from a general decline in
interest rates, or a combination of both. Conversely, capital depreciation may
result, for example, from a lowered credit standing or a general rise in
interest rates, or a combination of both. There is no assurance that the
objectives will be achieved.
 
    The higher yields sought by the Fund are generally obtainable from
securities rated in the lower categories by recognized rating services. The Fund
seeks high current income by investing principally in fixed-income securities
rated Baa or lower by Moody's Investors Service, Inc. ("Moody's"), or BBB or
lower by Standard & Poor's Corporation ("Standard & Poor's"). Fixed-income
securities rated Baa by Moody's or BBB by Standard & Poor's have speculative
characteristics greater than those of more highly rated bonds, while
fixed-income securities rated Ba or BB or lower by Moody's and Standard &
Poor's, respectively, are considered to be speculative investments. Furthermore,
the Fund does not have any minimum quality rating standard for its investments.
As such, the Fund may invest in securities rated as low as Caa, Ca or C by
Moody's or CCC, CC, C or C1 by Standard & Poor's. Fixed-income securities rated
Caa or Ca by Moody's may already be in default on payment of interest or
principal, while bonds rated C by Moody's, their lowest bond rating, can be
regarded as having extremely poor prospects of ever attaining any real
investment standing. Bonds rated C1 by Standard & Poor's, their lowest bond
rating, are no longer making interest payments. For a further discussion of the
characteristics and risks associated with high yield securities, see "Special
Investment Considerations" below. A description of corporate bond ratings is
contained in the Appendix.
 
    Non-rated securities will also be considered for investment by the Fund when
the Investment Manager believes that the financial condition of the issuers of
such securities, or the protection afforded by the terms of the securities
themselves, makes them appropriate investments for the Fund.
 
8
<PAGE>
    In circumstances where the Investment Manager determines that investment in
municipal obligations would facilitate the Fund's ability to accomplish its
investment objectives, it may invest up to 10% of its total assets in such
obligations, including municipal bonds issued at a discount.
 
    All fixed-income securities are subject to two types of risks: the credit
risk and the interest rate risk. The credit risk relates to the ability of the
issuer to meet interest or principal payments or both as they come due.
Generally, higher yielding bonds are subject to a credit risk to a greater
extent than higher quality bonds. The interest rate risk refers to the
fluctuations in net asset value of any portfolio of fixed-income securities
resulting solely from the inverse relationship between price and yield of fixed-
income securities; that is, when the general level of interest rates rises, the
prices of outstanding fixed-income securities generally decline, and when
interest rates fall, prices generally rise.
 
    The ratings of fixed-income securities by Moody's and Standard & Poor's are
a generally accepted barometer of credit risk. However, as the creditworthiness
of issuers of lower-rated fixed-income securities is more problematical than
that of issuers of higher-rated fixed-income securities, the achievement of the
Fund's investment objective will be more dependent upon the Investment Manager's
own credit analysis than would be the case with a mutual fund investing
primarily in higher quality bonds. The Investment Manager will utilize a
security's credit rating as simply one indication of an issuer's
creditworthiness and will principally rely upon its own analysis of any security
currently held by the Fund or potentially purchasable by the Fund for its
portfolio.
 
    In determining which securities to purchase or hold for the Fund's portfolio
and in seeking to reduce credit and interest rate risks, the Investment Manager
will rely on information from various sources, including: the rating of the
security; research, analysis and appraisals of brokers and dealers, including
Dean Witter Reynolds Inc. and other broker-dealer affiliates of the Investment
Manager; the views of others regarding economic developments and interest rate
trends, and the Investment Manager's own analysis of factors it deems relevant.
The extent to which the Investment Manager is successful in reducing
depreciation or losses arising from either interest rate or credit risks depends
in part on the Investment Manager's portfolio management skills and judgment in
evaluating the factors affecting the value of securities. No assurance can be
given regarding the degree of success that will be achieved.
 
SPECIAL RISK CONSIDERATIONS
 
The net asset value of the Fund's shares will fluctuate with changes in the
market value of its portfolio securities. The Fund's yield will also vary based
on the yield of the Fund's portfolio securities.
 
    Because of the special nature of the Fund's investment in high yield
securities, commonly known as junk bonds, the Investment Manager must take
account of certain special considerations in assessing the risks associated with
such investments. Although the growth of the high yield securities market in the
1980s had paralleled a long economic expansion, recently many issuers have been
affected by adverse economic and market conditions. It should be recognized that
an economic downturn or increase in interest rates is likely to have a negative
effect on the high yield bond market and on the value of the high yield
securities held by the Fund, as well as on the ability of the securities'
issuers to repay principal and interest on their borrowings.
 
    The prices of high yield securities have been found to be less sensitive to
changes in prevailing interest rates than higher-rated investments, but are
likely to be more sensitive to adverse economic changes or individual corporate
developments. During an economic downturn or substantial period of rising
interest rates, highly leveraged issuers may experience financial stress which
would adversely affect their ability to service their principal and interest
payment obligations, to meet their projected business goals or to obtain
additional financing. If the issuer of a fixed-income security owned by the Fund
defaults, the Fund may incur additional expenses to seek recovery. In addition,
periods of economic uncertainty and change can be expected to result in an
increased volatility of market prices of high yield securities and a concomitant
volatility in the net asset value of a share of the Fund. Moreover, the market
prices of certain of the Fund's portfolio securities which are structured as
zero coupon and payment-in-kind securities are affected to a greater extent by
interest rate changes and thereby tend to be more volatile than securities which
pay interest periodically and in cash (see "Dividends, Distributions and Taxes"
for a discussion of the tax ramifications of investments in such securities).
 
    The secondary market for high yield securities may be less liquid than the
markets for higher quality securities and, as such, may have an adverse effect
on the market prices of certain securities. The limited liquidity of the market
may also adversely affect the ability of the Fund's Directors to arrive at a
fair value for certain high yield securities at certain times and could make it
difficult for the Fund to sell certain securities. In addition, new laws and
potential new laws may have an adverse effect upon the value of high yield
securities and a concomitant negative impact upon the net asset value of a share
of the Fund.
 
    During the fiscal year ended August 31, 1998, the monthly dollar weighted
average ratings of the debt obligations held by the Fund, expressed as a
percentage of the Fund's total investments, were as follows:
 
                                                                               9
<PAGE>
 
<TABLE>
<CAPTION>
                                    PERCENTAGE OF
RATINGS                           TOTAL INVESTMENTS
- --------------------------------  ------------------
<S>                               <C>
AAA/Aaa.........................           4.3%
AA/Aa...........................           0.0%
A/A.............................          15.4%
BBB/Baa.........................           0.5%
BB/Ba...........................           4.4%
B/B.............................          60.4%
CCC/Caa.........................           3.2%
CC/Ca...........................           0.5%
C/C.............................           0.2%
D...............................           0.2%
Unrated.........................          10.9%
</TABLE>
 
    Consistent with its primary investment objective, the Fund anticipates that,
under normal conditions, at least 65% of the value of its total assets will be
invested in the lower-rated and non-rated fixed-income securities previously
described. However, when the difference between yields derived from such
securities and those derived from higher rated issues are relatively narrow, the
Fund may invest in the higher rated issues since they may provide similar yields
with somewhat less risk. Fixed-income securities appropriate for the Fund may
include both convertible and nonconvertible debt securities and preferred stock.
 
    Pending investment of proceeds from the sale of shares of the Fund or of its
portfolio securities or at other times when market conditions dictate a more
"defensive" investment strategy, the Fund may invest without limit in money
market instruments, including commercial paper of corporations organized under
the laws of any state or political subdivision of the United States,
certificates of deposit, bankers' acceptances and other obligations of domestic
banks or domestic branches of foreign banks, or foreign branches of domestic
banks, in each case having total assets of at least $500 million, and
obligations issued or guaranteed by the United States Government (including zero
coupon securities), or foreign governments or their respective instrumentalities
or agencies. The yield on these securities will generally tend to be lower than
the yield on other securities to be purchased by the Fund. To the extent the
Fund purchases Eurodollar certificates of deposit issued by foreign branches of
domestic United States banks, consideration will be given to their domestic
marketability, the lower reserve requirements normally mandated for overseas
banking operations, the possible impact of interruptions in the flow of
international currency transactions and economic developments which might
adversely affect the payment of principal or interest.
 
PUBLIC UTILITIES.  The Fund's investments in public utilities, if any, may be
subject to certain risks incurred by the Fund due to Federal, State or municipal
regulatory changes, insufficient rate increases or cost overruns.
 
REPURCHASE AGREEMENTS.  The Fund may enter into repurchase agreements, which may
be viewed as a type of secured lending by the Fund, and which typically involve
the acquisition by the Fund of debt securities, from a selling financial
institution such as a bank, savings and loan association or broker-dealer. The
agreement provides that the Fund will sell back to the institution, and that the
institution will repurchase, the underlying security at a specified price and at
a fixed time in the future, usually not more than seven days from the date of
purchase. While repurchase agreements involve certain risks not associated with
direct investments in debt securities, including the risk of default or
bankruptcy of the selling institution, the Fund follows procedures designed to
minimize such risks.
 
WHEN-ISSUED AND DELAYED DELIVERY SECURITIES.  The Fund may purchase securities
on a when-issued or delayed delivery basis; i.e., delivery and payment can take
place a month or more after the date of the transaction. These securities are
subject to market fluctuation and no interest accrues to the purchaser prior to
settlement. At the time the Fund makes the commitment to purchase such
securities, it will record the transaction and thereafter reflect the value,
each day, of such security in determining its net asset value. An increase in
the percentage of the Fund's assets committed to the purchase of securities on a
when-issued or delayed delivery basis may increase the volatility of the Fund's
net asset value.
 
WHEN, AS AND IF ISSUED SECURITIES.  The Fund may purchase securities on a "when,
as and if issued" basis under which the issuance of the security depends upon
the occurrence of a subsequent event, such as approval of a merger, corporate
reorganization, leveraged buyout or debt restructuring. If the anticipated event
does not occur and the securities are not issued, the Fund will have lost an
investment opportunity. There is no overall limit on the percentage of the
Fund's assets which may be committed to the purchase of securities on a "when,
as and if issued" basis. An increase in the percentage of the Fund's assets
committed to the purchase of securities on a "when, as and if issued" basis may
increase the volatility of its net asset value.
 
FOREIGN SECURITIES.  The Fund may invest up to 20% of its total assets in
fixed-income securities issued by foreign governments and other foreign issuers
and in foreign currency issues of domestic issuers, but not more than 10% of its
total assets in such securities, whether issued by a foreign or domestic issuer,
which are denominated in foreign currency. Foreign securities investments may be
affected by changes in currency rates or exchange control regulations, changes
in governmental administration or economic or monetary policy (in the United
States and abroad) or changed circumstances in dealings between nations. Costs
will be incurred in connection with conversions between various currencies held
by the Fund. When purchasing foreign securities, the Fund will generally enter
into foreign currency exchange transactions or forward foreign exchange
contracts to facilitate settlement. The Fund will utilize forward foreign
exchange contracts in these instances as an attempt to limit the effect of
changes in the
 
10
<PAGE>
relationship between the U.S. dollar and the foreign currency during the period
between the trade date and settlement date for the transaction.
 
    Investments in foreign securities will also occasion risks relating to
political and economic developments abroad, including the possibility of
expropriations or confiscatory taxation, limitations on the use or transfer of
Fund assets and any effects of foreign social, economic or political
instability. Foreign companies are not subject to the regulatory requirements of
U.S. companies and, as such, there may be less publicly available information
about such companies. Moreover, foreign companies are not subject to uniform
accounting, auditing and financial reporting standards and requirements
comparable to those applicable to U.S. companies. Finally, in the event of a
default of any foreign debt obligations, it may be more difficult for the Fund
to obtain or enforce a judgment against the issuers of such securities.
 
    Securities of foreign issuers may be less liquid than comparable securities
of U.S. issuers and, as such, their price changes may be more volatile.
Furthermore, foreign exchanges and broker-dealers are generally subject to less
government and exchange scrutiny and regulation than their American
counterparts. Brokerage commissions, dealer concessions and other transaction
costs may be higher on foreign markets than in the U.S. In addition, differences
in clearance and settlement procedures on foreign markets may occasion delays in
settlements of the Fund's trades effected in such markets. As such, the
inability to dispose of portfolio securities due to settlement delays could
result in losses to the Fund due to subsequent declines in value of such
securities and the inability of the Fund to make intended security purchases due
to settlement problems could result in a failure of the Fund to make potentially
advantageous investments.
 
    Many European countries are about to adopt a single European currency, the
euro (the "Euro Conversion"). The consequences of the Euro Conversion for
foreign exchange rates, interest rates and the value of European securities
eligible for purchase by the Fund are presently unclear. Such consequences may
adversely affect the value and/or increase the volatility of securities held by
the Fund.
 
COMMON STOCKS.  The Fund may invest in common stocks in an amount up to 20% of
its total assets. The Fund may directly purchase common stocks on the open
market. In addition, the Fund may acquire common stocks when they are included
in a unit with fixed-income securities purchased by the Fund; when fixed-income
securities held by the Fund are converted to equity issues; when the Fund
exercises a warrant; and when the Fund purchases the common stock of companies
involved in takeovers or recapitalizations, where the issuer or a stockholder
has offered, or pursuant to a "going private" transaction is effecting, a
transaction involving the issuance of newly issued fixed-income securities to
the holders of such common stock.
 
    The prices of common stock are generally more volatile than those of
fixed-income securities. Moreover, not all common stock pay dividends and those
that do generally pay lower amounts than most fixed-income securities. The Fund
will only purchase common stocks directly when the Investment Manager believes
that their purchase will assist the Fund in meeting its investment objectives.
 
ZERO COUPON SECURITIES.  A portion of the fixed-income securities purchased by
the Fund may be zero coupon securities. Such securities are purchased at a
discount from their face amount, giving the purchaser the right to receive their
full value at maturity. The interest earned on such securities is, implicitly,
automatically compounded and paid out at maturity. While such compounding at a
constant rate eliminates the risk of receiving lower yields upon reinvestment of
interest if prevailing interest rates decline, the owner of a zero coupon
security will be unable to participate in higher yields upon reinvestment of
interest received on interest-paying securities if prevailing interest rates
rise.
 
    A zero coupon security pays no interest to its holder during its life.
Therefore, to the extent the Fund invests in zero coupon securities, it will not
receive current cash available for distribution to shareholders. In addition,
zero coupon securities are subject to substantially greater price fluctuations
during periods of changing prevailing interest rates than are comparable
securities which pay interest on a current basis. Current federal tax law
requires that a holder (such as the Fund) of a zero coupon security accrue a
portion of the discount at which the security was purchased as income each year
even though the Fund receives no interest payments in cash on the security
during the year.
 
FUTURES CONTRACTS AND OPTIONS ON FUTURES.  The Fund may invest in financial
futures contracts ("futures contracts") and related options thereon. The Fund
may sell a futures contract or a call option thereon or purchase a put option on
such futures contract, if the Investment Manager anticipates interest rates to
rise, as a hedge against a decrease in the value of the Fund's portfolio
securities. If the Investment Manager anticipates that interest rates will
decline, the Fund may purchase a futures contract or a call option thereon or
sell a put option on such futures contract to protect against an increase in the
price of the securities the Fund intends to purchase. These futures contracts
and related options thereon will be used only as a hedge against anticipated
interest rate changes.
 
    The Fund may not enter into futures contracts or purchase related options
thereon if immediately thereafter the amount committed to margin plus the amount
paid for premiums for unexpired options on futures contracts exceeds 5% of the
value of the Fund's total assets. The Fund may not purchase or sell futures
contracts or related options thereon if, immediately thereafter, more than
one-third of its net assets would be hedged.
 
                                                                              11
<PAGE>
OPTIONS.  The Fund may purchase or sell (write) listed options on debt
securities as a means of achieving additional return or of hedging the value of
the Fund's portfolio. The Fund may only write covered options which are listed
on national securities exchanges. The Fund may not write covered options in an
amount exceeding 20% of the value of its total assets. The Fund may only buy
options which are listed on national securities exchanges. The Fund will not
purchase options if, as a result, the aggregate cost of all outstanding options
exceeds 10% of the Fund's total assets.
 
    For a discussion of futures and options, including the risks of such
transactions, see the Statement of Additional Information.
 
PRIVATE PLACEMENTS.  The Fund may invest up to 5% of its total assets in
securities which are subject to restrictions on resale because they have not
been registered under the Securities Act of 1933, as amended (the "Securities
Act"), or which are otherwise not readily marketable. These securities are
generally referred to as private placements or restricted securities.
Limitations on the resale of such securities may have an adverse effect on their
marketability, and may prevent the Fund from disposing of them promptly at
reasonable prices. The Fund may have to bear the expense of registering such
securities for resale and the risk of substantial delays in effecting such
registration.
 
    The Securities and Exchange Commission has adopted Rule 144A under the
Securities Act, which permits the Fund to sell restricted securities to
qualified institutional buyers without limitation. The Investment Manager,
pursuant to procedures adopted by the Board of Directors of the Fund, will make
a determination as to the liquidity of each restricted security purchased by the
Fund. If a restricted security is determined to be "liquid," such security will
not be considered to be "restricted" for purposes of the above-disclosed 5%
limitation and will not be included within the category "illiquid securities,"
which under current policy may not exceed 15% of the Fund's total assets.
However, investing in Rule 144A securities could have the effect of increasing
the level of Fund illiquidity to the extent the Fund, at a particular point of
time, may be unable to find qualified institutional buyers interested in
purchasing such securities.
 
YEAR 2000.  The investment management services provided to the Fund by the
Investment Manager and the services provided to shareholders by the Distributor
and the Transfer Agent depend on the smooth functioning of their computer
systems. Many computer software systems in use today cannot recognize the year
2000, but revert to 1900 or some other date, due to the manner in which dates
were encoded and calculated. That failure could have a negative impact on the
handling of securities trades, pricing and account services. The Investment
Manager, the Distributor and the Transfer Agent have been actively working on
necessary changes to their own computer systems to prepare for the year 2000 and
expect that their systems will be adapted before that date, but there can be no
assurance that they will be successful, or that interaction with other
non-complying computer systems will not impair their services at that time.
 
    In addition, it is possible that the markets for securities in which the
Fund invests may be detrimentally affected by computer failures throughout the
financial services industry beginning January 1, 2000. Improperly functioning
trading systems may result in settlement problems and liquidity issues. In
addition, corporate and governmental data processing errors may result in
production problems for individual companies and overall economic uncertainties.
Earnings of individual issuers will be affected by remediation costs, which may
be substantial and may be reported inconsistently in U.S. and foreign financial
statements. Accordingly, the Fund's investments may be adversely affected.
 
PORTFOLIO MANAGEMENT
 
The Fund is actively managed by the Investment Manager with a view to achieving
the Fund's investment objective. The Fund is managed within MSDW Advisors'
Taxable Income Group, which manages 21 funds and fund portfolios with
approximately $14 billion in assets at September 30, 1998. Peter M. Avelar,
Senior Vice President of MSDW Advisors and a member of MSDW Advisors' Taxable
Fixed-Income Group, has been the primary portfolio manager of the Fund since
January, 1991 and has been managing portfolios consisting of fixed-income and
equity securities at MSDW Advisors for over five years.
 
    Securities purchased by the Fund are, generally, sold
by dealers acting as principal for their own accounts. Pursuant to an order
issued by the Securities and Exchange Commission, the Fund may effect principal
transactions in certain money market instruments with Dean Witter Reynolds Inc.
In addition, the Fund may incur brokerage commissions on transactions conducted
through Dean Witter Reynolds Inc., Morgan Stanley & Co. Incorporated and other
brokers and dealers that are affiliates of MSDW Advisors.
 
    Although the Fund does not intend to engage in substantial short-term
trading, it may sell portfolio securities without regard to the length of time
that they have been held, in order to take advantage of new investment
opportunities or yield differentials, or because the Fund desires to preserve
gains or limit losses due to changing economic conditions, interest rate trends,
or the financial condition of the issuer. The Fund's portfolio turnover rate for
the fiscal year ended August 31, 1998 was 66.26%. The Fund will incur
underwriting discount costs (on underwritten securities) and brokerage costs
commensurate with its portfolio turnover rate. See "Dividends, Distributions and
Taxes" for a discussion of the tax implications of the Fund's trading policy.
 
12
<PAGE>
    Except as otherwise noted, all investment policies and practices discussed
above are not fundamental policies of the Fund and, as such may be changed
without shareholder approval.
 
INVESTMENT RESTRICTIONS
- --------------------------------------------------------------------------------
 
The investment restrictions listed below are among the restrictions that have
been adopted by the Fund as fundamental policies. Under the Investment Company
Act of 1940, as amended (the "Act"), a fundamental policy may not be changed
without the vote of a majority of the outstanding voting securities of the Fund,
as defined in the Act.
 
    The Fund may not:
 
        1. Acquire common stocks in excess of 20% of its total assets.
 
        2. Invest more than 5% of its total assets in the securities of any one
    issuer (other than obligations of, or guaranteed by, the United States
    Government, its agencies or instrumentalities).
 
        3. Purchase more than 10% of the voting securities, or more than 10% of
    any class of securities, of any issuer. For purposes of this restriction,
    all outstanding debt securities of an issuer are considered as one class and
    all preferred stocks of an issuer are considered as one class.
 
        4. Invest more than 25% of its total assets in securities of issuers in
    any one industry. For purposes of this restriction, gas, electric, water and
    telephone utilities will each be treated as being a separate industry. This
    restriction does not apply to obligations issued or guaranteed by the United
    States Government or its agencies or instrumentalities.
 
        5. Invest more than 5% of its total assets in securities of companies
    having a record, together with predecessors, of less than three years of
    continuous operation. This restriction shall not apply to any obligation of
    the United States Government, its agencies or instrumentalities.
 
    Notwithstanding any other investment policy or restriction, the Fund may
seek to achieve its investment objectives by investing all or substantially all
of its assets in another investment company having substantially the same
investment objectives and policies as the Fund.
 
PURCHASE OF FUND SHARES
- --------------------------------------------------------------------------------
 
GENERAL
 
The Fund offers each class of its shares for sale to the public on a continuous
basis. Pursuant to a Distribution Agreement between the Fund and Morgan Stanley
Dean Witter Distributors Inc. ("MSDW Distributors" or the "Distributor"), an
affiliate of the Investment Manager, shares of the Fund are distributed by the
Distributor and offered by Dean Witter Reynolds Inc. ("DWR"), a selected dealer
and subsidiary of Morgan Stanley Dean Witter & Co. and other dealers who have
entered into selected dealer agreements with the Distributor ("Selected
Broker-Dealers"). It is anticipated that DWR will undergo a change of corporate
name which is expected to incorporate the brand name of "Morgan Stanley Dean
Witter," pending approval of various regulatory authorities. The principal
executive office of the Distributor is located at Two World Trade Center, New
York, New York 10048.
 
    The Fund offers four classes of shares (each, a "Class"). Class A shares are
sold to investors with an initial sales charge that declines to zero for larger
purchases; however, Class A shares sold without an initial sales charge are
subject to a contingent deferred sales charge ("CDSC") of 1.0% if redeemed
within one year of purchase, except for certain specific circumstances. Class B
shares are sold without an initial sales charge but are subject to a CDSC
(scaled down from 5.0% to 1.0%) payable upon most redemptions within six years
after purchase. (Class B shares purchased by certain qualified plans are subject
to a CDSC scaled down from 2.0% to 1.0% if redeemed within three years after
purchase.) Class C shares are sold without an initial sales charge but are
subject to a CDSC of 1.0% on most redemptions made within one year after
purchase. Class D shares are sold without an initial sales charge or CDSC and
are available only to investors meeting an initial investment minimum of $5
million ($25 million for certain qualified plans), and to certain other limited
categories of investors. At the discretion of the Board of Directors of the
Fund, Class A shares may be sold to categories of investors in addition to those
set forth in this prospectus at net asset value without a front-end sales
charge, and Class D shares may be sold to certain other categories of investors,
in each case as may be described in the then current prospectus of the Fund. See
"Alternative Purchase Arrangements-- Selecting a Particular Class" for a
discussion of factors to consider in selecting which Class of shares to
purchase.
 
    The minimum initial purchase is $1,000 for each Class of shares, although
Class D shares are only available to persons investing $5 million ($25 million
for certain qualified plans) or more and to certain other limited categories of
investors. For the purpose of meeting the minimum $5 million (or $25 million)
initial investment for Class D shares, and subject to the $1,000 minimum initial
investment for each Class of the Fund, an investor's existing holdings of Class
A shares of the Fund and other Morgan Stanley Dean Witter Funds that are
multiple class funds
 
                                                                              13
<PAGE>
("Morgan Stanley Dean Witter Multi-Class Funds") and shares of Morgan Stanley
Dean Witter Funds sold with a front-end sales charge ("FSC Funds") and
concurrent investments in Class D shares of the Fund and other Morgan Stanley
Dean Witter Multi-Class Funds will be aggregated. Subsequent purchases of $100
or more may be made by sending a check, payable to Morgan Stanley Dean Witter
High Yield Securities Inc., directly to Morgan Stanley Dean Witter Trust FSB
(the "Transfer Agent" or "MSDW Trust") at P.O. Box 1040, Jersey City, N.J. 07303
or by contacting a Morgan Stanley Dean Witter Financial Advisor or other
Selected Broker-Dealer representative. When purchasing shares of the Fund,
investors must specify whether the purchase is for Class A, Class B, Class C or
Class D shares. If no Class is specified, the Transfer Agent will not process
the transaction until the proper Class is identified. The minimum initial
purchase in the case of investments through EasyInvest-SM-, an automatic
purchase plan (see "Shareholder Services"), is $100, provided that the schedule
of automatic investments will result in investments totalling at least $1,000
within the first twelve months. The minimum initial purchase in the case of an
"Education IRA" is $500, if the Distributor has reason to believe that
additional investments will increase the investment in the account to $1,000
within three years. In the case of investments pursuant to (i) Systematic
Payroll Deduction plans (including Individual Retirement plans), (ii) the MSDW
Advisors mutual fund asset allocation program and (iii) fee-based programs
approved by the Distributor, pursuant to which participants pay an asset based
fee for services, in the nature of investment advisory, administrative and/or
brokerage services, the Fund, in its discretion, may accept investments without
regard to any minimum amounts which would otherwise be required provided, in the
case of Systematic Payroll Deduction Plans, that if the Distributor has reason
to believe that additional purchases will increase the amount of the purchase of
shares in all accounts under such plans to at least $1,000. Certificates for
shares purchased will not be issued unless a request is made by the shareholder
in writing to the Transfer Agent.
 
    Shares are sold through the Distributor on a normal three business day
settlement basis; that is, payment is due on the third business day (settlement
date) after the order is placed with the Distributor. Since DWR and other
Selected Broker-Dealers forward investors' funds on settlement date, they will
benefit from the temporary use of the funds if payment is made prior thereto. As
noted above, orders placed directly with the Transfer Agent must be accompanied
by payment. Investors will be entitled to receive income dividends and capital
gains distributions if their order is received by the close of business on the
day prior to the record date for such dividends and distributions. Sales
personnel of a Selected Broker-Dealer are compensated for selling shares of the
Fund by the Distributor or any of its affiliates and/or the Selected
Broker-Dealer. In addition, some sales personnel of the Selected Broker-Dealer
will receive various types of non-cash compensation as special sales incentives,
including trips, educational and/ or business seminars and merchandise. The Fund
and the Distributor reserve the right to reject any purchase order.
 
ALTERNATIVE PURCHASE ARRANGEMENTS
 
The Fund offers several Classes of shares to investors designed to provide them
with the flexibility of selecting an investment best suited to their needs. The
general public is offered three Classes of shares: Class A shares, Class B
shares and Class C shares, which differ principally in terms of sales charges
and rate of expenses to which they are subject. A fourth Class of shares, Class
D shares, is offered only to limited categories of investors (see "No Load
Alternative--Class D Shares" below).
 
    Each Class A, Class B, Class C or Class D share of the Fund represents an
identical interest in the investment portfolio of the Fund except that Class A,
Class B and Class C shares bear the expenses of the ongoing shareholder service
fees, Class B and Class C shares bear the expenses of the ongoing distribution
fees and Class A, Class B and Class C shares which are redeemed subject to a
CDSC bear the expense of the additional incremental distribution costs resulting
from the CDSC applicable to shares of those Classes. The ongoing distribution
fees that are imposed on Class A, Class B and Class C shares will be imposed
directly against those Classes and not against all assets of the Fund and,
accordingly, such charges against one Class will not affect the net asset value
of any other Class or have any impact on investors choosing another sales charge
option. See "Plan of Distribution" and "Redemptions and Repurchases."
 
    Set forth below is a summary of the differences between the Classes and the
factors an investor should consider when selecting a particular Class. This
summary is qualified in its entirety by detailed discussion of each Class that
follows this summary.
 
CLASS A SHARES.  Class A shares are sold at net asset value plus an initial
sales charge of up to 4.25%. The initial sales charge is reduced for certain
purchases. Investments of $1 million or more (and investments by certain other
limited categories of investors) are not subject to any sales charges at the
time of purchase but are subject to a CDSC of 1.0% on redemptions made within
one year after purchase, except for certain specific circumstances. Class A
shares are also subject to a 12b-1 fee of up to 0.25% of the average daily net
assets of the Class. See "Initial Sales Charge Alternative--Class A Shares."
 
CLASS B SHARES.  Class B shares are offered at net asset value with no initial
sales charge but are subject to a CDSC (scaled down from 5.0% to 1.0%) if
redeemed within six years of purchase. (Class B shares purchased by certain
qualified plans are subject to a CDSC scaled down from 2.0% to 1.0% if redeemed
within three years after purchase.) This CDSC may be waived for certain
redemptions.
 
14
<PAGE>
Class B shares are also subject to an annual 12b-1 fee of 0.75% of the average
daily net assets of Class B. The Class B shares' distribution fee will cause
that Class to have higher expenses and pay lower dividends than Class A or Class
D shares.
 
    After approximately ten (10) years, Class B shares will convert
automatically to Class A shares of the Fund, based on the relative net asset
values of the shares of the two Classes on the conversion date. In addition, a
certain portion of Class B shares that have been acquired through the
reinvestment of dividends and distributions will be converted at that time. See
"Contingent Deferred Sales Charge Alternative--Class B Shares."
 
CLASS C SHARES.  Class C shares are sold at net asset value with no initial
sales charge but are subject to a CDSC of 1.0% on redemptions made within one
year after purchase. This CDSC may be waived for certain redemptions. They are
subject to an annual 12b-1 fee of up to 0.85% of the average daily net assets of
the Class C shares. The Class C shares' distribution fee may cause that Class to
have higher expenses and pay lower dividends than Class A or Class D shares. See
"Level Load Alternative--Class C Shares."
 
CLASS D SHARES.  Class D shares are available only to limited categories of
investors (see "No Load Alternative-- Class D Shares" below). Class D shares are
sold at net asset value with no initial sales charge or CDSC. They are not
subject to any 12b-1 fees. See "No Load Alternative-- Class D Shares."
 
SELECTING A PARTICULAR CLASS.  In deciding which Class of Fund shares to
purchase, investors should consider the following factors, as well as any other
relevant facts and circumstances:
 
    The decision as to which Class of shares is more beneficial to an investor
depends on the amount and intended length of his or her investment. Investors
who prefer an initial sales charge alternative may elect to purchase Class A
shares. Investors qualifying for significantly reduced or, in the case of
purchases of $1 million or more, no initial sales charges may find Class A
shares particularly attractive because similar sales charge reductions are not
available with respect to Class B or Class C shares. Moreover, Class A shares
are subject to lower ongoing expenses than are Class B or Class C shares over
the term of the investment. As an alternative, Class B and Class C shares are
sold without any initial sales charge so the entire purchase price is
immediately invested in the Fund. Any investment return on these additional
investment amounts may partially or wholly offset the higher annual expenses of
these Classes. Because the Fund's future return cannot be predicted, however,
there can be no assurance that this would be the case.
 
    Finally, investors should consider the effect of the CDSC period and any
conversion rights of the Classes in the context of their own investment time
frame. For example, although Class C shares are subject to a significantly lower
CDSC upon redemptions, they do not, unlike Class B shares, convert into Class A
shares after approximately ten years, and, therefore, are subject to an ongoing
12b-1 fee of 0.85% (rather than the 0.25% fee applicable to Class A shares) for
an indefinite period of time. Thus, Class B shares may be more attractive than
Class C shares to investors with longer term investment outlooks. Other
investors, however, may elect to purchase Class C shares if, for example, they
determine that they do not wish to be subject to a front-end sales charge and
they are uncertain as to the length of time they intend to hold their shares.
 
    For the purpose of meeting the $5 million (or $25 million) minimum
investment amount for Class D shares, holdings of Class A shares in all Morgan
Stanley Dean Witter Multi-Class Funds, shares of FSC Funds and shares of Morgan
Stanley Dean Witter Funds for which such shares have been exchanged will be
included together with the current investment amount.
 
    Sales personnel may receive different compensation for selling each Class of
shares. Investors should understand that the purpose of a CDSC is the same as
that of the initial sales charge in that the sales charges applicable to each
Class provide for the financing of the distribution of shares of that Class.
 
    Set forth below is a chart comparing the sales charge, 12b-1 fees and
conversion options applicable to each Class of shares:
 
<TABLE>
<CAPTION>
                                                   CONVERSION
  CLASS          SALES CHARGE         12b-1 FEE      FEATURE
<C>        <S>                        <C>        <C>
    A      Maximum 4.25% initial        0.25%          No
           sales charge reduced for
           purchases of $25,000 and
           over; shares sold without
           an initial sales charge
           generally subject to a
           1.0% CDSC during first
           year.
    B      Maximum 5.0% CDSC during     0.75%    B shares
           the first year decreasing             convert to A
           to 0 after six years                  shares
                                                 automatically
                                                 after
                                                 approximately
                                                 ten years
    C      1.0% CDSC during first       0.85%          No
           year
    D                None               None           No
</TABLE>
 
    See "Purchase of Fund Shares" and "The Fund and its Management" for a
complete description of the sales charges and service and distribution fees for
each Class of shares and "Determination of Net Asset Value," "Dividends,
Distributions and Taxes" and "Shareholder Services--Exchange Privilege" for
other differences between the Classes of shares.
 
                                                                              15
<PAGE>
INITIAL SALES CHARGE ALTERNATIVE-- CLASS A SHARES
 
Class A shares are sold at net asset value plus an initial sales charge. In some
cases, reduced sales charges may be available, as described below. Investments
of $1 million or more (and investments by certain other limited categories of
investors) are not subject to any sales charges at the time of purchase but are
subject to a CDSC of 1.0% on redemptions made within one year after purchase
(calculated from the last day of the month in which the shares were purchased),
except for certain specific circumstances. The CDSC will be assessed on an
amount equal to the lesser of the current market value or the cost of the shares
being redeemed. The CDSC will not be imposed (i) in the circumstances set forth
below in the section "Contingent Deferred Sales Charge Alternative--Class B
Shares-- CDSC Waivers," except that the references to six years in the first
paragraph of that section shall mean one year in the case of Class A shares, and
(ii) in the circumstances identified in the section "Additional Net Asset Value
Purchase Options" below. Class A shares are also subject to an annual 12b-1 fee
of up to 0.25% of the average daily net assets of the Class.
 
    The offering price of Class A shares will be the net asset value per share
next determined following receipt of an order (see "Determination of Net Asset
Value" below), plus a sales charge (expressed as a percentage of the offering
price) on a single transaction as shown in the following table:
 
<TABLE>
<CAPTION>
                                         SALES CHARGE
                             -------------------------------------
                               PERCENTAGE OF       APPROXIMATE
         AMOUNT OF            PUBLIC OFFERING     PERCENTAGE OF
    SINGLE TRANSACTION             PRICE         AMOUNT INVESTED
- ---------------------------  -----------------  ------------------
<S>                          <C>                <C>
Less than $25,000..........          4.25%               4.44%
$25,000 but less
  than $50,000.............          4.00%               4.17%
$50,000 but less
  than $100,000............          3.50%               3.63%
$100,000 but less
  than $250,000............          2.75%               2.83%
$250,000 but less
  than $1 million..........          1.75%               1.78%
$1 million and over........             0                   0
</TABLE>
 
    Upon notice to all Selected Broker-Dealers, the Distributor may reallow up
to the full applicable sales charge as shown in the above schedule during
periods specified in such notice. During periods when 90% or more of the sales
charge is reallowed, such Selected Broker-Dealers may be deemed to be
underwriters as that term is defined in the Securities Act of 1933.
 
    The above schedule of sales charges is applicable to purchases in a single
transaction by, among others: (a) an individual; (b) an individual, his or her
spouse and their children under the age of 21 purchasing shares for his, her or
their own accounts; (c) a trustee or other fiduciary purchasing shares for a
single trust estate or a single fiduciary account; (d) a pension, profit-sharing
or other employee benefit plan qualified or non-qualified under Section 401 of
the Internal Revenue Code; (e) tax-exempt organizations enumerated in Section
501(c)(3) or (13) of the Internal Revenue Code; (f) employee benefit plans
qualified under Section 401 of the Internal Revenue Code of a single employer or
of employers who are "affiliated persons" of each other within the meaning of
Section 2(a)(3)(c) of the Act; and for investments in Individual Retirement
Accounts of employees of a single employer through Systematic Payroll Deduction
plans; or (g) any other organized group of persons, whether incorporated or not,
provided the organization has been in existence for at least six months and has
some purpose other than the purchase of redeemable securities of a registered
investment company at a discount.
 
COMBINED PURCHASE PRIVILEGE.  Investors may have the benefit of reduced sales
charges in accordance with the above schedule by combining purchases of Class A
shares of the Fund in single transactions with the purchase of Class A shares of
other Morgan Stanley Dean Witter Multi-Class Funds and shares of FSC Funds. The
sales charge payable on the purchase of the Class A shares of the Fund, the
Class A shares of the other Morgan Stanley Dean Witter Multi-Class Funds and the
shares of the FSC Funds will be at their respective rates applicable to the
total amount of the combined concurrent purchases of such shares.
 
RIGHT OF ACCUMULATION.  The above persons and entities may benefit from a
reduction of the sales charges in accordance with the above schedule if the
cumulative net asset value of Class A shares purchased in a single transaction,
together with shares of the Fund and other Morgan Stanley Dean Witter Funds
previously purchased at a price including a front-end sales charge (including
shares of the Fund and other Morgan Stanley Dean Witter Funds acquired in
exchange for those shares, and including in each case shares acquired through
reinvestment of dividends and distributions), which are held at the time of such
transaction, amounts to $25,000 or more. If such investor has a cumulative net
asset value of shares of FSC Funds and Class A and Class D shares that, together
with the current investment amount, is equal to at least $5 million ($25 million
for certain qualified plans), such investor is eligible to purchase Class D
shares subject to the $1,000 minimum initial investment requirement of that
Class of the Fund. See "No Load Alternative--Class D Shares" below.
 
    The Distributor must be notified by DWR or a Selected Broker-Dealer or the
shareholder at the time a purchase order is placed that the purchase qualifies
for the reduced charge under the Right of Accumulation. Similar notification
must be made in writing by the dealer or shareholder when such an order is
placed by mail. The reduced sales charge will not be granted if: (a) such
notification is not furnished at the time of the order; or (b) a review of the
records of the Selected Broker-Dealer or the Transfer Agent fails to confirm the
investor's represented holdings.
 
16
<PAGE>
LETTER OF INTENT.  The foregoing schedule of reduced sales charges will also be
available to investors who enter into a written Letter of Intent providing for
the purchase, within a thirteen-month period, of Class A shares of the Fund from
DWR or other Selected Broker-Dealers. The cost of Class A shares of the Fund or
shares of other Morgan Stanley Dean Witter Funds which were previously purchased
at a price including a front-end sales charge during the 90-day period prior to
the date of receipt by the Distributor of the Letter of Intent, or of Class A
shares of the Fund or shares of other Morgan Stanley Dean Witter Funds acquired
in exchange for shares of such funds purchased during such period at a price
including a front-end sales charge, which are still owned by the shareholder,
may also be included in determining the applicable reduction.
 
ADDITIONAL NET ASSET VALUE PURCHASE OPTIONS.  In addition to investments of $1
million or more, Class A shares also may be purchased at net asset value by the
following:
 
    (1) trusts for which MSDW Trust (which is an affiliate of the Investment
Manager) provides discretionary trustee services;
 
    (2) persons participating in a fee-based program approved by the
Distributor, pursuant to which such persons pay an asset based fee for services
in the nature of investment advisory, administrative and/or brokerage services
(such investments are subject to all of the terms and conditions of such
programs, which may include termination fees, mandatory redemption upon
termination and such other circumstances as specified in the programs'
agreements, and restrictions on transferability of Fund shares);
 
    (3) employer-sponsored 401(k) and other plans qualified under Section 401(a)
of the Internal Revenue Code ("Qualified Retirement Plans") with at least 200
eligible employees and for which MSDW Trust serves as Trustee or DWR's
Retirement Plan Services serves as recordkeeper pursuant to a written
Recordkeeping Services Agreement;
 
    (4) Qualified Retirement Plans for which MSDW Trust serves as Trustee or
DWR's Retirement Plan Services serves as recordkeeper pursuant to a written
Recordkeeping Services Agreement whose Class B shares have converted to Class A
shares, regardless of the plan's asset size or number of eligible employees;
 
    (5) investors who are clients of a Morgan Stanley Dean Witter Financial
Advisor who joined Morgan Stanley Dean Witter from another investment firm
within six months prior to the date of purchase of Fund shares by such
investors, if the shares are being purchased with the proceeds from a redemption
of shares of an open-end proprietary mutual fund of the Financial Advisor's
previous firm which imposed either a front-end or deferred sales charge,
provided such purchase was made within sixty days after the redemption and the
proceeds of the redemption had been maintained in the interim in cash or a money
market fund; and
 
    (6) other categories of investors, at the discretion of the Board, as
disclosed in the then current prospectus of the Fund.
 
    No CDSC will be imposed on redemptions of shares purchased pursuant to
paragraphs (1), (2) or (5), above.
 
    For further information concerning purchases of the Fund's shares, contact
DWR or another Selected Broker-Dealer or consult the Statement of Additional
Information.
 
CONTINGENT DEFERRED SALES CHARGE ALTERNATIVE--CLASS B SHARES
 
Class B shares are sold at net asset value next determined without an initial
sales charge so that the full amount of an investor's purchase payment may be
immediately invested in the Fund. A CDSC, however, will be imposed on most Class
B shares redeemed within six years after purchase. The CDSC will be imposed on
any redemption of shares if after such redemption the aggregate current value of
a Class B account with the Fund falls below the aggregate amount of the
investor's purchase payments for Class B shares made during the six years (or,
in the case of shares held by certain Qualified Retirement Plans, three years)
preceding the redemption. In addition, Class B shares are subject to an annual
12b-1 fee of 0.75% of the average daily net assets of Class B.
 
    Except as noted below, Class B shares of the Fund which are held for six
years or more after purchase (calculated from the last day of the month in which
the shares were purchased) will not be subject to any CDSC upon redemption.
Shares redeemed earlier than six years after purchase may, however, be subject
to a CDSC which will be a percentage of the dollar amount of shares redeemed and
will be assessed on an amount equal to the lesser of the current market value or
the cost of the shares being redeemed. The size of this percentage will depend
upon how long the shares have been held, as set forth in the following table:
 
<TABLE>
<CAPTION>
          YEAR SINCE PURCHASE             CDSC AS A PERCENTAGE
              PAYMENT MADE                 OF AMOUNT REDEEMED
- ----------------------------------------  ---------------------
<S>                                       <C>
First...................................             5.0%
Second..................................             4.0%
Third...................................             3.0%
Fourth..................................             2.0%
Fifth...................................             2.0%
Sixth...................................             1.0%
Seventh and thereafter..................             None
</TABLE>
 
    In the case of Class B shares of the Fund purchased on or after July 28,
1997 by Qualified Retirement Plans for which MSDW Trust serves as Trustee or
DWR's Retirement Plan Services serves as recordkeeper pursuant to a written
Recordkeeping Services Agreement, shares held for three years or more after
purchase (calculated as described in the paragraph above) will not be subject to
any CDSC upon redemption. However, shares redeemed earlier
 
                                                                              17
<PAGE>
than three years after purchase may be subject to a CDSC (calculated as
described in the paragraph above), the percentage of which will depend on how
long the shares have been held, as set forth in the following table:
 
<TABLE>
<CAPTION>
          YEAR SINCE PURCHASE             CDSC AS A PERCENTAGE
              PAYMENT MADE                 OF AMOUNT REDEEMED
- ----------------------------------------  ---------------------
<S>                                       <C>
First...................................             2.0%
Second..................................             2.0%
Third...................................             1.0%
Fourth and thereafter...................             None
</TABLE>
 
    Class B shares of the Fund issued in exchange for shares of Dean Witter High
Income Securities ("High Income Securities") in connection with the
Reorganization of High Income Securities with the Fund on November 10, 1997,
that were subject to the lower CDSC schedule of High Income Securities (as
described below), will continue to be subject to that lower CDSC schedule unless
(i) such shares are subsequently exchanged for shares of a fund with a higher
CDSC schedule or (ii) having been exchanged for shares of Morgan Stanley Dean
Witter Global Short-Term Income Fund Inc. ("Global Short-Term") or an Exchange
Fund (as defined below in "Shareholder Services--Exchange Privilege") are
re-exchanged back into the Fund. Under such circumstances, the CDSC schedule
applicable to shares of the fund with the higher CDSC schedule acquired in the
exchange will apply to redemptions of such fund's shares or, in the case of
shares of Global Short-Term or any of the Exchange Funds acquired in an exchange
and then subsequently re-exchanged back into the Fund, the CDSC schedule set
forth in the above table will apply to redemptions of any of such shares. The
CDSC schedule applicable to High Income Securities was as follows: Shares held
for five years or more after purchase (calculated as described in the paragraph
above) are not subject to any CDSC upon redemption. However, shares redeemed
earlier than five years after purchase may be subject to a CDSC (calculated as
described in the paragraph above), the percentage of which depends on how long
the shares have been held, as set forth in the following table:
 
<TABLE>
<CAPTION>
          YEAR SINCE PURCHASE             CDSC AS A PERCENTAGE
              PAYMENT MADE                 OF AMOUNT REDEEMED
- ----------------------------------------  ---------------------
<S>                                       <C>
First...................................             4.0%
Second..................................             3.0%
Third...................................             2.0%
Fourth..................................             2.0%
Fifth...................................             1.0%
Sixth and thereafter....................             None
</TABLE>
 
CDSC WAIVERS.  A CDSC will not be imposed on: (i) any amount which represents an
increase in value of shares purchased within the six years (or, in the case of
shares held by certain Qualified Retirement Plans, three years) preceding the
redemption; (ii) the current net asset value of shares purchased more than six
years (or, in the case of shares held by certain Qualified Retirement Plans,
three years) prior to the redemption; and (iii) the current net asset value of
shares purchased through reinvestment of dividends or distributions and/or
shares acquired in exchange for shares of FSC Funds or of other Morgan Stanley
Dean Witter Funds acquired in exchange for such shares. Moreover, in determining
whether a CDSC is applicable it will be assumed that amounts described in (i),
(ii) and (iii) above (in that order) are redeemed first.
 
    In addition, the CDSC, if otherwise applicable, will be waived in the case
of:
 
    (1) redemptions of shares held at the time a shareholder dies or becomes
disabled, only if the shares are:  (a) registered either in the name of an
individual shareholder (not a trust), or in the names of such shareholder and
his or her spouse as joint tenants with right of survivorship; or  (b) held in a
qualified corporate or self-employed retirement plan, Individual Retirement
Account ("IRA") or Custodial Account under Section 403(b)(7) of the Internal
Revenue Code ("403(b) Custodial Account"), provided in either case that the
redemption is requested within one year of the death or initial determination of
disability;
 
    (2) redemptions in connection with the following retirement plan
distributions:  (a) lump-sum or other distributions from a qualified corporate
or self-employed retirement plan following retirement (or, in the case of a "key
employee" of a "top heavy" plan, following attainment of age 59 1/2); (b)
distributions from an IRA or 403(b) Custodial Account following attainment of
age 59 1/2; or  (c) a tax-free return of an excess contribution to an IRA;
 
    (3) all redemptions of shares held for the benefit of a participant in a
Qualified Retirement Plan, which offers investment companies managed by the
Investment Manager or its subsidiary, MSDW Services, as self-directed investment
alternatives and for which MSDW Trust serves as Trustee or DWR's Retirement Plan
Services serves as recordkeeper pursuant to a written Recordkeeping Services
Agreement ("Eligible Plan"), provided that either:  (a) the plan continues to be
an Eligible Plan after the redemption; or  (b) the redemption is in connection
with the complete termination of the plan involving the distribution of all plan
assets to participants; and
 
    (4) certain redemptions pursuant to the Fund's Systematic Withdrawal Plan
(see "Shareholder Services--Systematic Withdrawal Plan").
 
    With reference to  (1) above, for the purpose of determining disability, the
Distributor utilizes the definition of disability contained in Section 72(m)(7)
of the Internal Revenue Code, which relates to the inability to engage in
gainful employment. With reference to  (2) above, the term "distribution" does
not encompass a direct transfer of IRA, 403(b) Custodial Account or retirement
plan assets to a successor custodian or trustee. All waivers will be granted
only following receipt by the Distributor of confirmation of the shareholder's
entitlement.
 
18
<PAGE>
CONVERSION TO CLASS A SHARES.  Class B shares will convert automatically to
Class A shares, based on the relative net asset values of the shares of the two
Classes on the conversion date, which will be approximately ten (10) years after
the date of the original purchase. The ten year period is calculated from the
last day of the month in which the shares were purchased or, in the case of
Class B shares acquired through an exchange or a series of exchanges, from the
last day of the month in which the original Class B shares were purchased. The
conversion of shares will take place in the month following the tenth
anniversary of the purchase. There will also be converted at that time such
proportion of Class B shares acquired through automatic reinvestment of
dividends and distributions owned by the shareholder as the total number of his
or her Class B shares converting at the time bears to the total number of
outstanding Class B shares purchased and owned by the shareholder. In the case
of Class B shares held by a Qualified Retirement Plan for which MSDW Trust
serves as Trustee or DWR's Retirement Plan Services serves as recordkeeper
pursuant to a written Recordkeeping Services Agreement, the plan is treated as a
single investor and all Class B shares will convert to Class A shares on the
conversion date of the first shares of a Morgan Stanley Dean Witter Multi-Class
Fund purchased by that plan. In the case of Class B shares previously exchanged
for shares of an "Exchange Fund" (see "Shareholder Services-- Exchange
Privilege"), the period of time the shares were held in the Exchange Fund
(calculated from the last day of the month in which the Exchange Fund shares
were acquired) is excluded from the holding period for conversion. If those
shares are subsequently re-exchanged for Class B shares of a Morgan Stanley Dean
Witter Multi-Class Fund, the holding period resumes on the last day of the month
in which Class B shares are reacquired.
 
    If a shareholder has received share certificates for Class B shares, such
certificates must be delivered to the Transfer Agent at least one week prior to
the date for conversion. Class B shares evidenced by share certificates that are
not received by the Transfer Agent at least one week prior to any conversion
date will be converted into Class A shares on the next scheduled conversion date
after such certificates are received.
 
    Effectiveness of the conversion feature is subject to the continuing
availability of a ruling of the Internal Revenue Service or an opinion of
counsel that (i) the conversion of shares does not constitute a taxable event
under the Internal Revenue Code, (ii) Class A shares received on conversion will
have a basis equal to the shareholder's basis in the converted Class B shares
immediately prior to the conversion, and (iii) Class A shares received on
conversion will have a holding period that includes the holding period of the
converted Class B shares. The conversion feature may be suspended if the ruling
or opinion is no longer available. In such event, Class B shares would continue
to be subject to Class B 12b-1 fees.
 
LEVEL LOAD ALTERNATIVE-- CLASS C SHARES
 
Class C shares are sold at net asset value next determined without an initial
sales charge but are subject to a CDSC of 1.0% on most redemptions made within
one year after purchase (calculated from the last day of the month in which the
shares were purchased). The CDSC will be assessed on an amount equal to the
lesser of the current market value or the cost of the shares being redeemed. The
CDSC will not be imposed in the circumstances set forth above in the section
"Contingent Deferred Sales Charge Alternative-- Class B Shares--CDSC Waivers,"
except that the references to six years in the first paragraph of that section
shall mean one year in the case of Class C shares. Class C shares are subject to
an annual 12b-1 fee of up to 0.85% of the average daily net assets of the Class.
Unlike Class B shares, Class C shares have no conversion feature and,
accordingly, an investor that purchases Class C shares will be subject to 12b-1
fees applicable to Class C shares for an indefinite period subject to annual
approval by the Fund's Board of Directors and regulatory limitations.
 
NO LOAD ALTERNATIVE-- CLASS D SHARES
 
Class D shares are offered without any sales charge on purchase or redemption
and without any 12b-1 fee. Class D shares are offered only to investors meeting
an initial investment minimum of $5 million ($25 million for Qualified
Retirement Plans for which MSDW Trust serves as Trustee and DWR's Retirement
Plan Services serves as recordkeeper pursuant to a written Recordkeeping
Services Agreement) and the following categories of investors: (i) investors
participating in the MSDW Advisors mutual fund asset allocation program pursuant
to which such per-
sons pay an asset based fee; (ii) persons participating in a fee-based program
approved by the Distributor, pursuant to which such persons pay an asset based
fee for services in the nature of investment advisory, administrative and/or
brokerage services (subject to all of the terms and conditions of such programs
referred to in (i) and (ii) above, which may include termination fees, mandatory
redemption upon termination and such other circumstances as specified in the
programs' agreements, and restrictions on transferability of Fund shares); (iii)
employee benefit plans maintained by Morgan Stanley Dean Witter & Co. or any of
its subsidiaries for the benefit of certain employees of Morgan Stanley Dean
Witter & Co. and its subsidiaries; (iv) certain Unit Investment Trusts sponsored
by DWR; (v) certain other open-end investment companies whose shares are
distributed by the Distributor; (vi) investors who were shareholders of Dean
Witter Retirement Series on September 11, 1998 (with respect to additional
purchases for their former Dean Witter Retirement Series accounts); and (vii)
other categories of investors, at the discretion of the Board, as disclosed in
the then current prospectus of the Fund. All shares of the Fund held prior to
July 28, 1997 have
 
                                                                              19
<PAGE>
been designated Class D shares. Additional investments in Class D shares by
shareholders holding such shares may only be made if those shareholders are
otherwise eligible to purchase Class D shares. However, shareholders holding
such shares will receive the benefit of the value of such shares towards reduced
sales charges on purchases of Class A shares pursuant to the Fund's "Right of
Accumulation" (see "Initial Sales Charge Alternative--Class A Shares--Right of
Accumulation"). Investors who require a $5 million (or $25 million) minimum
initial investment to qualify to purchase Class D shares may satisfy that
requirement by investing that amount in a single transaction in Class D shares
of the Fund and other Morgan Stanley Dean Witter Multi-Class Funds, subject to
the $1,000 minimum initial investment required for that Class of the Fund. In
addition, for the purpose of meeting the $5 million (or $25 million) minimum
investment amount, holdings of Class A shares in all Morgan Stanley Dean Witter
Multi-Class Funds, shares of FSC Funds and shares of Morgan Stanley Dean Witter
Funds for which such shares have been exchanged will be included together with
the current investment amount. If a shareholder redeems Class A shares and
purchases Class D shares, such redemption may be a taxable event.
 
PLAN OF DISTRIBUTION
 
The Fund has adopted a Plan of Distribution pursuant to Rule 12b-1 under the Act
with respect to the distribution of Class A, Class B and Class C shares of the
Fund. In the case of Class A and Class C shares, the Plan provides that the Fund
will reimburse the Distributor and others for the expenses of certain activities
and services incurred by them specifically on behalf of those shares.
Reimbursements for these expenses will be made in monthly payments by the Fund
to the Distributor, which will in no event exceed amounts equal to payments at
the annual rates of 0.25% and 0.85% of the average daily net assets of Class A
and Class C, respectively. In the case of Class B shares, the Plan provides that
the Fund will pay the Distributor a fee, which is accrued daily and paid
monthly, at the annual rate of 0.75% of the average daily net assets of Class B.
The fee is treated by the Fund as an expense in the year it is accrued. In the
case of Class A shares, the entire amount of the fee currently represents a
service fee within the meaning of the NASD guidelines. In the case of Class B
and Class C shares, a portion of the fee payable pursuant to the Plan, equal to
0.20% and 0.25% of the average daily net assets of each of these Classes,
respectively, is currently characterized as a service fee. A service fee is a
payment made for personal service and/or the maintenance of shareholder
accounts.
 
    Additional amounts paid under the Plan in the case of Class B and Class C
shares are paid to the Distributor for services provided and the expenses borne
by the Distributor and others in the distribution of the shares of those
Classes, including the payment of commissions for sales of the shares of those
Classes and incentive compensation to and expenses of Morgan Stanley Dean Witter
Financial Advisors and others who engage in or support distribution of shares or
who service shareholder accounts, including overhead and telephone expenses;
printing and distribution of prospectuses and reports used in connection with
the offering of the Fund's shares to other than current shareholders; and
preparation, printing and distribution of sales literature and advertising
materials. In addition, the Distributor may utilize fees paid pursuant to the
Plan in the case of Class B shares to compensate DWR and other Selected
Broker-Dealers for their opportunity costs in advancing such amounts, which
compensation would be in the form of a carrying charge on any unreimbursed
expenses.
 
    For the fiscal year ended August 31, 1998, Class B shares of the Fund
accrued payments under the Plan amounting to $10,737,221 which amount is equal
to 0.74% of the average daily net assets of Class B for the fiscal year. For the
fiscal year ended August 31, 1998, Class A and Class C shares of the Fund
accrued payments under the Plan amounting to $51,000 and $281,533, respectively,
which amounts are equal to 0.24% and 0.85% of the average daily net assets of
Class A and Class C, respectively for such fiscal year.
 
    In the case of Class B shares, at any given time, the expenses in
distributing Class B shares of the Fund may be in excess of the total of (i) the
payments made by the Fund pursuant to the Plan, and (ii) the proceeds of CDSCs
paid by investors upon the redemption of Class B shares. For example, if $1
million in expenses in distributing Class B shares of the Fund had been incurred
and $750,000 had been received as described in (i) and (ii) above, the excess
expense would amount to $250,000. The Distributor has advised the Fund that such
excess amounts including the carrying charge described above totalled
$50,323,518 at August 31, 1998, which was equal to 2.86% of the net assets of
Class B on such date. Of this amount, $36,793,648 represents excess distribution
expenses of Dean Witter High Income Securities, the net assets of which were
combined with those of the Fund on November 10, 1997 pursuant to an Agreement
and Plan of Reorganization. Because there is no requirement under the Plan that
the Distributor be reimbursed for all distribution expenses or any requirement
that the Plan be continued from year to year, such excess amount does not
constitute a liability of the Fund. Although there is no legal obligation for
the Fund to pay expenses incurred in excess of payments made to the Distributor
under the Plan, and the proceeds of CDSCs paid by investors upon redemption of
shares, if for any reason the Plan is terminated the Directors will consider at
that time the manner in which to treat such expenses. Any cumulative expenses
incurred, but not yet recovered through distribution fees or CDSCs, may or may
not be recovered through future distribution fees or CDSCs.
 
    In the case of Class A and Class C shares, expenses incurred pursuant to the
Plan in any calendar year in excess
 
20
<PAGE>
of 0.25% or 0.85% of the average daily net assets of Class A or Class C,
respectively, will not be reimbursed by the Fund through payments in any
subsequent year, except that expenses representing a gross sales commission
credited to Morgan Stanley Dean Witter Financial Advisors and other Selected
Broker-Dealer representatives at the time of sale may be reimbursed in the
subsequent calendar year. The Distributor has advised the Fund that unreimbursed
expenses representing a gross sales commission credited to Morgan Stanley Dean
Witter Financial Advisors and other Selected Broker-Dealer representatives at
the time of sale totalled $175,137 in the case of Class C at December 31, 1997,
which was equal to 0.70% of the net assets of Class C on such date, and that
there were no such expenses which may be reimbursed in the subsequent year in
the case of Class A on such date. No interest or other financing charges will be
incurred on any Class A or Class C distribution expenses incurred by the
Distributor under the Plan or on any unreimbursed expenses due to the
Distributor pursuant to the Plan.
 
DETERMINATION OF NET ASSET VALUE
 
The net asset value per share is determined once daily at 4:00 p.m., New York
time on each day that the New York Stock Exchange is open (or, on days when the
New York Stock Exchange closes prior to 4:00 p.m., at such earlier time), by
taking the net assets of the Fund, dividing by the number of shares outstanding
and adjusting to the nearest cent. The assets belonging to the Class A, Class B,
Class C and Class D shares will be invested together in a single portfolio. The
net asset value of each Class, however, will be determined separately by
subtracting each Class's accrued expenses and liabilities. The net asset value
per share will not be determined on Good Friday and on such other federal and
non-federal holidays as are observed by the New York Stock Exchange.
 
    In the calculation of the Fund's net asset value: (1) an equity portfolio
security listed or traded on the New York or American Stock Exchange or other
domestic or foreign exchange is valued at its latest sale price on that exchange
prior to the time assets are valued; (if there were no sales that day, the
security is valued at the latest bid price); and (2) all other portfolio
securities for which over-the-counter market quotations are readily available
are valued at the latest bid price. When market quotations are not readily
available, including circumstances under which it is determined by the
Investment Manager that sale or bid prices are not reflective of a security's
market value, portfolio securities are valued at their fair value as determined
in good faith under procedures established by and under the general supervision
of the Fund's Board of Directors (valuation of securities for which market
quotations are not readily available may be based upon current market prices of
securities which are comparable in coupon, rating and maturity or an appropriate
matrix utilizing similar factors).
 
    Certain of the Fund's portfolio securities may be valued by an outside
pricing service approved by the Fund's Directors. The pricing service may
utilize a matrix system incorporating security quality, maturity and coupon as
the evaluation model parameters, and/or research evaluations by its staff,
including review of broker-dealer market price quotations, in determining what
it believes is the fair valuation of the portfolio securities valued by such
pricing service.
 
    Municipal securities will be valued for the Fund by an outside computer
matrix pricing service approved by the Board of Directors. Periodically, the
Investment Manager and the Board of Directors review the continued
appropriateness of the prices obtained through the service.
 
    Short-term debt securities with remaining maturities of 60 days or less at
the time of purchase are valued at amortized cost, unless the Board determines
such does not reflect the securities' fair value, in which case these securities
will be valued at their fair market value as determined by the Board of
Directors. Other short-term debt securities will be valued on a marked-to-market
basis until such time as they reach a maturity of 60 days, whereupon they will
be valued at amortized cost using their value on the 61st day unless the
Directors determine such does not reflect the securities' market value, in which
case these securities will be valued at their fair market value as determined by
the Board of Directors. Listed options on debt securities are valued at the
latest sale price on the exchange on which they are listed unless no sales of
such options have taken place that day, in which case, they will be valued at
the mean between their closing bid and asked prices. Unlisted options on debt
securities and all options on equity securities are valued at the mean between
their latest bid and asked price. Futures are valued at the latest sale price on
the commodities exchange on which they trade unless the Directors determine that
such price does not reflect their market value, in which case they will be
valued at their fair value as determined by the Board of Directors. All other
securities and other assets are valued at their fair value as determined in good
faith under procedures established by and under the supervision of the Board of
Directors.
 
SHAREHOLDER SERVICES
- --------------------------------------------------------------------------------
 
AUTOMATIC INVESTMENT OF DIVIDENDS AND DISTRIBUTIONS.  All income dividends and
capital gains distributions are automatically paid in full and fractional shares
of the applicable Class of the Fund (or, if specified by the shareholder, in
shares of any other open-end Morgan Stanley Dean Witter Fund), unless the
shareholder requests that they be paid in cash. Shares so acquired are acquired
at net asset value and are not subject to the imposition of a front-end sales
charge or a CDSC (see "Redemptions and Repurchases").
 
                                                                              21
<PAGE>
INVESTMENT OF DISTRIBUTIONS RECEIVED IN CASH.  Any shareholder who receives a
cash payment representing a dividend or capital gains distribution may invest
such dividend or distribution in shares of the applicable Class at the net asset
value next determined after receipt by the Transfer Agent, by returning the
check or the proceeds to the Transfer Agent within thirty days after the payment
date. Shares so acquired are acquired at net asset value and are not subject to
the imposition of a front-end sales charge or a CDSC (see "Redemptions and
Repurchases").
 
EASYINVEST.-SM-  Shareholders may subscribe to EasyInvest, an automatic purchase
plan which provides for any amount from $100 to $5,000 to be transferred
automatically from a checking or savings account or following redemption of
shares of a Morgan Stanley Dean Witter money market fund, on a semi-monthly,
monthly or quarterly basis, to the Fund's Transfer Agent for investment in
shares of the Fund (see "Purchase of Fund Shares" and "Redemptions and
Repurchases--Involuntary Redemption").
 
SYSTEMATIC WITHDRAWAL PLAN.  A systematic withdrawal plan (the "Withdrawal
Plan") is available for shareholders whose shares of Morgan Stanley Dean Witter
Funds have an aggregate value of $10,000 or more. Shares of any Fund from which
redemptions will be made pursuant to the Plan must have a value of $1,000 or
more (referred to as a "SWP Fund"). The required share values are determined on
the date the shareholder establishes the Withdrawal Plan. The Withdrawal Plan
provides for monthly, quarterly, semi-annual or annual payments in any amount
not less than $25, or in any whole percentage of the value of the SWP Funds'
shares, on an annualized basis. Any applicable CDSC will be imposed on shares
redeemed under the Withdrawal Plan (see "Purchase of Fund Shares"), except that
the CDSC, if any, will be waived on redemptions under the Withdrawal Plan of up
to 12% annually of the value of each SWP Fund account based on the share values
next determined after the shareholder establishes the Withdrawal Plan.
Redemptions for which this CDSC waiver policy applies may be in amounts up to 1%
per month, 3% per quarter, 6% semi-annually or 12% annually. Under this CDSC
waiver policy, amounts withdrawn each period will be paid by first redeeming
shares not subject to a CDSC because the shares were purchased by the
reinvestment of dividends or capital gains distributions, the CDSC period has
elapsed or some other waiver of the CDSC applies. If shares subject to a CDSC
must be redeemed, shares held for the longest period of time will be redeemed
first and continuing with shares held the next longest period of time until
shares held the shortest period of time are redeemed. Any shareholder
participating in the Withdrawal Plan will have sufficient shares redeemed from
his or her account so that the proceeds (net of any applicable CDSC) to the
shareholder will be the designated monthly, quarterly, semi-annual or annual
amount.
 
    A shareholder may suspend or terminate participation in the Withdrawal Plan
at any time. A shareholder who has suspended participation may resume payments
under the Withdrawal Plan, without requiring a new determination of the account
value for the 12% CDSC waiver. The Withdrawal Plan may be terminated or revised
at any time by the Fund.
 
    Prior to adding an additional SWP Fund to an existing Withdrawal Plan, the
required $10,000/$1,000 share values must be met, to be calculated on the date
the shareholder adds the additional SWP Fund. However, the addition of a new SWP
Fund will not change the account value for the 12% CDSC waiver for the SWP Funds
already participating in the Withdrawal Plan.
 
    Withdrawal Plan payments should not be considered dividends, yields or
income. If periodic Withdrawal Plan payments continuously exceed net investment
income and net capital gains, the shareholder's original investment will be
correspondingly reduced and ultimately exhausted. Each withdrawal constitutes a
redemption of shares and any gain or loss realized must be recognized for
federal income tax purposes.
 
    Shareholders should contact their Morgan Stanley Dean Witter Financial
Advisor or other Selected Broker-Dealer representative or the Transfer Agent for
further information about any of the above services.
 
TAX-SHELTERED RETIREMENT PLANS.  Retirement plans are available through the
Investment Manager for use by corporations, the self-employed, Individual
Retirement Accounts and Custodial Accounts under Section 403(b)(7) of the
Internal Revenue Code. Adoption of such plans should be on advice of legal
counsel or tax advisor.
 
    For further information regarding plan administration, custodial fees and
other details, investors should contact their Morgan Stanley Dean Witter
Financial Advisor or other Selected Broker-Dealer representative or the Transfer
Agent.
 
EXCHANGE PRIVILEGE
 
Shares of each Class may be exchanged for shares of the same Class of any other
Morgan Stanley Dean Witter Multi-Class Fund without the imposition of any
exchange fee. Shares may also be exchanged for shares of the following funds:
Morgan Stanley Dean Witter Short-Term U.S. Treasury Trust, Morgan Stanley Dean
Witter Limited Term Municipal Trust, Morgan Stanley Dean Witter Short-Term Bond
Fund, and five Morgan Stanley Dean Witter funds which are money market funds
(the "Exchange Funds"). Class A shares may also be exchanged for shares of
Morgan Stanley Dean Witter Multi-State Municipal Series Trust and Morgan Stanley
Dean Witter Hawaii Municipal Trust, which are Morgan Stanley Dean Witter Funds
sold with a front-end sales charge ("FSC Funds"). Exchanges may be made after
the shares of the Fund acquired by purchase (not by exchange or dividend
reinvestment) have been held for thirty days. There is no holding period for
exchanges of shares acquired by exchange or dividend reinvestment.
 
22
<PAGE>
    An exchange to another Morgan Stanley Dean Witter Multi-Class Fund, any FSC
Fund or any Exchange Fund that is not a money market fund is on the basis of the
next calculated net asset value per share of each fund after the exchange order
is received. When exchanging into a money market fund from the Fund, shares of
the Fund are redeemed out of the Fund at their next calculated net asset value
and the proceeds of the redemption are used to purchase shares of the money
market fund at their net asset value determined the following business day.
Subsequent exchanges between any of the money market funds and any of the Morgan
Stanley Dean Witter Multi-Class Funds, FSC Funds or any Exchange Fund that is
not a money market fund can be effected on the same basis.
 
    No CDSC is imposed at the time of any exchange of shares, although any
applicable CDSC will be imposed upon ultimate redemption. During the period of
time the shareholder remains in an Exchange Fund (calculated from the last day
of the month in which the Exchange Fund shares were acquired), the holding
period (for the purpose of determining the rate of the CDSC) is frozen. If those
shares are subsequently re-exchanged for shares of a Morgan Stanley Dean Witter
Multi-Class Fund, the holding period previously frozen when the first exchange
was made resumes on the last day of the month in which shares of a Morgan
Stanley Dean Witter Multi-Class Fund are reacquired. Thus, the CDSC is based
upon the time (calculated as described above) the shareholder was invested in
shares of a Morgan Stanley Dean Witter Multi-Class Fund (see "Purchase of Fund
Shares"). In the case of exchanges of Class A shares which are subject to a
CDSC, the holding period also includes the time (calculated as described above)
the shareholder was invested in shares of a FSC Fund. In the case of shares
exchanged into an Exchange Fund on or after April 23, 1990, upon a redemption of
shares which results in a CDSC being imposed, a credit (not to exceed the amount
of the CDSC) will be given in an amount equal to the Exchange Fund 12b-1
distribution fees incurred, if any, on or after that date which are attributable
to those shares. (Exchange Fund 12b-1 distribution fees are described in the
prospectuses for those funds.) Class B shares of the Fund acquired in exchange
for Class B shares of another Morgan Stanley Dean Witter Multi-Class Fund having
a different CDSC schedule than that of this Fund will be subject to the higher
CDSC schedule, even if such shares are subsequently re-exchanged for shares of
the fund with the lower CDSC schedule. Class B shares of the Fund issued in
exchange for shares of High Income Securities in connection with the
Reorganization that were subject to the lower CDSC schedule of High Income
Securities (as described above) will continue to be subject to that lower CDSC
schedule unless (i) such shares are subsequently exchanged for shares of a fund
with a higher CDSC schedule or (ii) having been exchanged for shares of Morgan
Stanley Dean Witter Global Short-Term Fund Inc. or an Exchange Fund are
re-exchanged back into the Fund. Under such circumstances, the CDSC schedule
applicable to shares of the fund with the higher CDSC schedule acquired in the
exchange will apply to redemptions of such fund's shares or, in the case of
shares of Morgan Stanley Dean Witter Global Short-Term Fund Inc. or any of the
Exchange Funds acquired in an exchange and then subsequently re-exchanged back
into the Fund, the Fund's CDSC schedule will apply to redemptions of any of such
shares.
 
ADDITIONAL INFORMATION REGARDING EXCHANGES.  Purchases and exchanges should be
made for investment purposes only. A pattern of frequent exchanges may be deemed
by the Investment Manager to be abusive and contrary to the best interests of
the Fund's other shareholders and, at the Investment Manager's discretion, may
be limited by the Fund's refusal to accept additional purchases and/or exchanges
from the investor. Although the Fund does not have any specific definition of
what constitutes a pattern of frequent exchanges, and will consider all relevant
factors in determining whether a particular situation is abusive and contrary to
the best interests of the Fund and its other shareholders, investors should be
aware that the Fund and each of the other Morgan Stanley Dean Witter Funds may
in their discretion limit or otherwise restrict the number of times this
Exchange Privilege may be exercised by any investor. Any such restriction will
be made by the Fund on a prospective basis only, upon notice to the shareholder
not later than ten days following such shareholder's most recent exchange. Also,
the Exchange Privilege may be terminated or revised at any time by the Fund
and/or any of such Morgan Stanley Dean Witter Funds for which shares of the Fund
have been exchanged, upon such notice as may be required by applicable
regulatory agencies. Shareholders maintaining margin accounts with DWR or
another Selected Broker-Dealer are referred to their Morgan Stanley Dean Witter
Financial Advisor or other Selected Broker-Dealer representative regarding
restrictions on exchange of shares of the Fund pledged in the margin account.
 
    The current prospectus for each fund describes its investment objective(s)
and policies, and shareholders should obtain a copy and examine it carefully
before investing. Exchanges are subject to the minimum investment requirement of
each Class of shares and any other conditions imposed by each fund. In the case
of a shareholder holding a share certificate or certificates, no exchanges may
be made until all applicable share certificates have been received by the
Transfer Agent and deposited in the shareholder's account. An exchange will be
treated for federal income tax purposes the same as a repurchase or redemption
of shares, on which the shareholder may realize a capital gain or loss. However,
the ability to deduct capital losses on an exchange may be limited in situations
where there is an exchange of shares within ninety days after the shares are
purchased. The Exchange Privilege is only available in states where an exchange
may legally be made.
 
    If DWR or another Selected Broker-Dealer is the current dealer of record and
its account numbers are part of the account information, shareholders may
initiate an exchange
 
                                                                              23
<PAGE>
of shares of the Fund for shares of any of the Morgan Stanley Dean Witter Funds
(for which the Exchange Privilege is available) pursuant to this Exchange
Privilege by contacting their Morgan Stanley Dean Witter Financial Advisor or
other Selected Broker-Dealer representative (no Exchange Privilege Authorization
Form is required). Other shareholders (and those shareholders who are clients of
DWR or other Selected Broker-Dealer but who wish to make exchanges directly by
telephoning the Transfer Agent) must complete and forward to the Transfer Agent
an Exchange Privilege Authorization form, copies of which may be obtained from
the Transfer Agent, to initiate an exchange. If the Authorization Form is used,
exchanges may be made in writing or by contacting the Transfer Agent at (800)
869-NEWS (toll-free).
 
    The Fund will employ reasonable procedures to confirm that exchange
instructions communicated over the telephone are genuine. Such procedures may
include requiring various forms of personal identification such as name, mailing
address, social security or other tax identification number and DWR or other
Selected Broker-Dealer account number (if any). Telephone instructions may also
be recorded. If such procedures are not employed, the Fund may be liable for any
losses due to unauthorized or fraudulent instructions.
 
    Telephone exchange instructions will be accepted if received by the Transfer
Agent between 9:00 a.m. and 4:00 p.m. New York time, on any day the New York
Stock Exchange is open. Any shareholder wishing to make an exchange who has
previously filed an Exchange Privilege Form and who is unable to reach the Fund
by telephone should contact his or her Morgan Stanley Dean Witter Financial
Advisor or other Selected Broker-Dealer representative, if appropriate, or make
a written exchange request. Shareholders are advised that during periods of
drastic economic or market changes, it is possible that the telephone exchange
procedures may be difficult to implement, although this has not been the
experience of the Morgan Stanley Dean Witter Funds in the past.
 
    Shareholders should contact their Morgan Stanley Dean Witter Financial
Advisor or other Selected Broker-Dealer representative or the Transfer Agent for
further information about the Exchange Privilege.
 
REDEMPTIONS AND REPURCHASES
- --------------------------------------------------------------------------------
 
REDEMPTION.  Shares of each Class of the Fund can be redeemed for cash at any
time at the current net asset value per share next determined less the amount of
any applicable CDSC in the case of Class A, Class B or Class C shares (see
"Purchase of Fund Shares"). If shares are held in a shareholder's account
without a stock certificate, a written request for redemption is required. If
certificates are held by the shareholder, the shares may be redeemed by
surrendering the certificates with a written request for redemption along with
any additional information requested by the Transfer Agent.
 
REPURCHASE.  DWR and other Selected Broker-Dealers are authorized to repurchase,
as agent for the Fund, shares represented by a stock certificate which is
delivered to any of their offices. Shares held in a shareholder's account
without a stock certificate may also be repurchased by DWR and other Selected
Broker-Dealers upon the telephonic request of the shareholder. The repurchase
price is the net asset value next determined (see "Purchase of Fund Shares")
after such repurchase order is received by DWR or other Selected Broker-Dealer
reduced by any applicable CDSC.
 
    The CDSC, if any, will be the only fee imposed by the Fund or the
Distributor. The offer by DWR and other Selected Broker-Dealers to repurchase
shares may be suspended without notice by them at any time. In that event,
shareholders may redeem their shares through the Fund's Transfer Agent as set
forth above under "Redemption."
 
PAYMENT FOR SHARES REDEEMED OR REPURCHASED.  Payment for shares presented for
repurchase or redemption will be made by check within seven days after receipt
by the Transfer Agent of the certificate and/or written request in good order.
Such payment may be postponed or the right of redemption suspended at times when
normal trading is not taking place on the New York Stock Exchange. If the shares
to be redeemed have recently been purchased by check, payment of the redemption
proceeds may be delayed for the minimum time needed to verify that the check
used for investment has been honored (not more than fifteen days from the time
of receipt of the check by the Transfer Agent). Shareholders maintaining margin
accounts with DWR and other Selected Broker Dealers are referred to their Morgan
Stanley Dean Witter Financial Advisor or other Selected Broker-Dealer
representative regarding restrictions on redemption of shares of the Fund
pledged in the margin account.
 
REINSTATEMENT PRIVILEGE.  A shareholder who has had his or her shares redeemed
or repurchased and has not previously exercised this reinstatement privilege
may, within 35 days after the date of the redemption or repurchase, reinstate
any portion or all of the proceeds of such redemption or repurchase in shares of
the Fund in the same Class from which such shares were redeemed or repurchased,
at their net asset value next determined after a reinstatement request, together
with the proceeds, is received by the Transfer Agent and receive a pro rata
credit for any CDSC paid in connection with such repurchase or redemption.
 
INVOLUNTARY REDEMPTION.  The Fund reserves the right, on sixty days' notice, to
redeem, at their net asset value, the shares of any shareholder (other than
shares held in an Individual Retirement Account or custodial account under
 
24
<PAGE>
Section 403(b)(7) of the Internal Revenue Code) whose shares due to redemptions
by the shareholder have a value of less than $100, or such lesser amount as may
be fixed by the Board of Directors or, in the case of an account opened through
EasyInvest-SM-, if after twelve months the shareholder has invested less than
$1,000 in the account. However, before the Fund redeems such shares and sends
the proceeds to the shareholder, it will notify the shareholder that the value
of the shares is less than the applicable amount and allow the shareholder sixty
days in which to make an additional investment in an amount which will increase
the value of the account to at least the applicable amount or more before the
redemption is processed. No CDSC will be imposed on any involuntary redemption.
 
DIVIDENDS, DISTRIBUTIONS AND TAXES
- --------------------------------------------------------------------------------
 
DIVIDENDS AND DISTRIBUTIONS.  The Fund declares dividends separately for each
Class of shares and intends to declare and pay monthly income dividends and to
distribute net short-term and net long-term capital gains, if any, at least once
each year. The Fund may, however, determine either to distribute or to retain
all or part of any long-term capital gains in any year for reinvestment.
 
    All dividends and capital gains distributions will be paid in additional
shares of the same Class and automatically credited to the shareholder's account
without issuance of a stock certificate unless the shareholder requests in
writing that all dividends be paid in cash. Shares acquired by dividend and
distribution reinvestments will not be subject to any front-end sales charge or
CDSC. Class B shares acquired through dividend and distribution reinvestments
will become eligible for conversion to Class A shares on a pro rata basis.
Distributions paid on Class A and Class D shares will be higher than for Class B
and Class C shares because distribution fees paid by Class B and Class C shares
are higher. (See "Shareholder Services--Automatic Investment of Dividends and
Distributions.")
 
TAXES.  Because the Fund intends to distribute all of its net investment income
and net capital gains to shareholders and otherwise continue to qualify as a
regulated investment company under Subchapter M of the Internal Revenue Code, it
is not expected that the Fund will be required to pay any Federal income tax on
such income and capital gains.
 
    With respect to the Fund's investments in zero coupon and payment-in-kind
bonds, the Fund accrues income prior to any actual cash payments by their
issuers. In order to continue to comply with Subchapter M of the Internal
Revenue Code and remain able to forego payment of Federal income tax on its
income and capital gains, the Fund must distribute all of its net investment
income, including income accrued from zero coupon and payment-in-kind bonds. As
such, the Fund may be required to dispose of some of its portfolio securities
under disadvantageous circumstances to generate the cash required for
distribution.
 
    Shareholders will normally have to pay Federal income taxes, and any
applicable state and/or local income taxes, on the dividends and distributions
they receive from the Fund. Such dividends and distributions, to the extent they
are derived from net investment income or net short-term capital gains, are
taxable to the shareholder as ordinary dividend income regardless of whether the
shareholder receives such distributions in additional shares or in cash. Any
dividends declared in the last calendar quarter of any year to shareholders of
record for that period which are paid in the following year prior to February 1
will be deemed received by the shareholder in the prior year. Since the Fund's
income is expected to be derived primarily from interest rather than dividends,
only a small portion, if any, of such dividends and distributions is expected to
be eligible for the Federal dividends received deduction available to
corporations.
 
    Distributions of net long-term capital gains, if any, are taxable to
shareholders as long-term capital gains regardless of how long a shareholder has
held the Fund's shares and regardless of whether the distribution is received in
additional shares or in cash. Capital gains distributions are not eligible for
the dividends received deduction. Capital gains may be generated by transactions
in options and futures contracts engaged in by the Fund. The Taxpayer Relief Act
reduces the maximum tax on long-term capital gains from 28% to 20%. The lower
rates do not apply to collectibles and certain other assets. Additionally, the
maximum capital gain rate for assets that are held more than 5 years and that
are acquired after December 31, 2000 is 18%.
 
    The Fund may at times make payments from sources other than income or net
capital gains. Payments from such sources will, in effect, represent a return of
a portion of each shareholder's investment. All, or a portion, of such payments
will not be taxable to shareholders.
 
    After the end of the calendar year, shareholders will receive a statement of
their dividends and capital gains distributions for tax purposes, including
information as to the portion taxable as ordinary income and the portion taxable
as capital gains.
 
    To avoid being subject to a 31% Federal backup withholding tax on taxable
dividends, capital gains distributions and the proceeds of redemptions and
repurchases, shareholders' taxpayer identification numbers must be furnished and
certified as to their accuracy.
 
    Shareholders should consult their tax advisors regarding specific questions
as to state or local taxes and as to the applicability of the foregoing to their
current federal tax situation.
 
                                                                              25
<PAGE>
PERFORMANCE INFORMATION
- --------------------------------------------------------------------------------
 
From time to time the Fund may quote its "yield" and/or its "total return" in
advertisements and sales literature. These figures are computed separately for
Class A, Class B, Class C and Class D shares. Both the yield and the total
return of the Fund are based on historical earnings and are not intended to
indicate future performance. The yield of each Class of the Fund will be
computed by dividing the Class's net investment income over a 30-day period by
an average value (using the average number of shares entitled to receive
dividends and the maximum offering price per share at the end of the period),
all in accordance with applicable regulatory requirements. Such amount will be
compounded for six months and then annualized for a twelve-month period to
derive the Fund's yield for each Class.
 
    The "average annual total return" of the Fund refers to a figure reflecting
the average annualized percentage increase (or decrease) in the value of an
initial investment in a Class of the Fund of $1,000 over periods of one, five
and ten years. Average annual total return reflects all income earned by the
Fund, any appreciation or depreciation of the Fund's assets, all expenses
incurred by the applicable Class and all sales charges incurred by shareholders,
for the stated periods. It also assumes reinvestment of all dividends and
distributions paid by the Fund.
 
    In addition to the foregoing, the Fund may advertise its total return for
each Class over different periods of time by means of aggregate, average,
year-by-year or other types of total return figures. Such calculations may or
may not reflect the deduction of any sales charge which, if reflected, would
reduce the performance quoted. The Fund may advertise the growth of hypothetical
investments of $10,000, $50,000 or $100,000 in each Class of shares of the Fund.
The Fund from time to time may also advertise its performance relative to
certain performance rankings and indexes compiled by independent organizations,
such as mutual fund performance rankings of Lipper Analytical Services, Inc.
 
    Prior to July 28, 1997, the Fund offered only one Class of shares. Because
the distribution arrangement for Class A most closely resembles the distribution
arrangement applicable prior to the implementation of multiple classes,
historical performance information may be restated to reflect the current
maximum sales charge applicable to Class A as well as the imposition of an
ongoing 12b-1 fee. In addition, because all shares of the Fund held prior to
July 28, 1997 have been designated Class D shares, the Fund's historical
performance may also be restated to reflect the absence of any sales charge in
the case of Class D shares.
 
ADDITIONAL INFORMATION
- --------------------------------------------------------------------------------
 
VOTING RIGHTS.  All shares of the Fund are of common stock of $0.01 par value
and are equal as to earnings, assets and voting privileges except that each
Class will have exclusive voting privileges with respect to matters relating to
distribution expenses borne solely by such Class or any other matter in which
the interests of one Class differ from the interests of any other Class. In
addition, Class B shareholders will have the right to vote on any proposed
material increase in Class A's expenses, if such proposal is submitted
separately to Class A shareholders. Also, as discussed herein, Class A, Class B
and Class C bear the expenses related to the distribution of their respective
shares.
 
    Under ordinary circumstances, the Fund is not required, nor does it intend,
to hold Annual Meetings of Stockholders. The Directors may call Special Meetings
of Stockholders for action by stockholder vote as may be required by the Act or
the Fund's By-Laws.
 
CODE OF ETHICS.  Directors, officers and employees of MSDW Advisors, MSDW
Services and MSDW Distributors are subject to a strict Code of Ethics adopted by
those companies. The Code of Ethics is intended to ensure that the interests of
shareholders and other clients are placed ahead of any personal interest, that
no undue personal benefit is obtained from a person's employment activities and
that actual and potential conflicts of interest are avoided. To achieve these
goals and comply with regulatory requirements, the Code of Ethics requires,
among other things, that personal securities transactions by employees of the
companies be subject to an advance clearance process to monitor that no Morgan
Stanley Dean Witter Fund is engaged at the same time in a purchase or sale of
the same security. The Code of Ethics bans the purchase of securities in an
initial public offering, and also prohibits engaging in futures and options
transactions and profiting on short-term trading (that is, a purchase within 60
days of a sale or a sale within 60 days of a purchase) of a security. In
addition, investment personnel may not purchase or sell a security for their
personal account within 30 days before or after any transaction in any Morgan
Stanley Dean Witter Fund managed by them. Any violations of the Code of Ethics
are subject to sanctions, including reprimand, demotion or suspension or
termination of employment. The Code of Ethics comports with regulatory
requirements and the recommendations in the 1994 report by the Investment
Company Institute Advisory Group on Personal Investing.
 
MASTER/FEEDER CONVERSION.  The Fund reserves the right to seek to achieve its
investment objectives by investing all of its investable assets in a
diversified, open-end management investment company having the same investment
objectives and policies and substantially the same investment restrictions as
those applicable to the Fund.
 
SHAREHOLDER INQUIRIES.  All inquiries regarding the Fund should be directed to
the Fund at the telephone numbers or address set forth on the front cover of
this Prospectus.
 
26
<PAGE>
APPENDIX -- RATINGS OF INVESTMENTS
- --------------------------------------------------------------------------------
 
MOODY'S INVESTORS SERVICE INC. ("MOODY'S")
 
                                  BOND RATINGS
 
<TABLE>
<S>        <C>
Aaa        Bonds which are rated Aaa are judged to be of the best quality. They carry the smallest
           degree of investment risk and are generally referred to as "gilt edge." Interest
           payments are protected by a large or by an exceptionally stable margin and principal is
           secure. While the various protective elements are likely to change, such changes as can
           be visualized are most unlikely to impair the fundamentally strong position of such
           issues.
Aa         Bonds which are rated Aa are judged to be of high quality by all standards. Together
           with the Aaa group they comprise what are generally known as high grade bonds. They are
           rated lower than the best bonds because margins of protection may not be as large as in
           Aaa securities or fluctuation of protective elements may be of greater amplitude or
           there may be other elements present which make the long-term risks appear somewhat
           larger than in Aaa securities.
A          Bonds which are rated A possess many favorable investment attributes and are to be
           considered as upper medium grade obligations. Factors giving security to principal and
           interest are considered adequate, but elements may be present which suggest a
           susceptibility to impairment sometime in the future.
Baa        Bonds which are rated Baa are 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.
           Bonds rated Aaa, Aa, A and Baa are considered investment grade bonds.
Ba         Bonds which are rated Ba are judged to have speculative elements; their future cannot be
           considered as well assured. Often the protection of interest and principal payments may
           be very moderate, and therefore not well safeguarded during both good and bad times over
           the future. Uncertainty of position characterizes bonds in this class.
B          Bonds which are rated B generally lack characteristics of desirable investments.
           Assurance of interest and principal payments or of maintenance of other terms of the
           contract over any long period of time may be small.
Caa        Bonds which are rated Caa are of poor standing. Such issues may be in default or there
           may be present elements of danger with respect to principal or interest.
Ca         Bonds which are rated Ca present obligations which are speculative in a high degree.
           Such issues are often in default or have other marked shortcomings.
C          Bonds which are rated C are the lowest rated class of bonds, and issues so rated can be
           regarded as having extremely poor prospects of ever attaining any real investment
           standing.
</TABLE>
 
    CONDITIONAL RATING:  Municipal bonds for which the security depends upon
    the completion of some act or the fulfillment of some condition are
    rated conditionally. These are bonds secured by (a) earnings of projects
    under construction, (b) earnings of projects unseasoned in operation
    experience, (c) rentals which begin when facilities are completed, or
    (d) payments to which some other limiting condition attaches.
    Parenthetical rating denotes probable credit stature upon completion of
    construction or elimination of basis of condition.
 
    RATING REFINEMENTS:  Moody's may apply numerical modifiers, 1, 2 and 3
    in each generic rating classification from Aa through B in its corporate
    and municipal bond rating system. The modifier 1 indicates that the
    security ranks in the higher end of its generic rating category; the
    modifier 2 indicates a mid-range ranking; and a modifier 3 indicates
    that the issue ranks in the lower end of its generic rating category.
 
                            COMMERCIAL PAPER RATINGS
 
    Moody's Commercial Paper ratings are opinions of the ability to repay
    punctually promissory obligations not having an original maturity in
    excess of nine months. Moody's employs the following three designations,
    all judged to be investment grade, to indicate the relative repayment
    capacity of rated issuers: Prime-1, Prime-2, Prime-3.
 
                                                                              27
<PAGE>
        Issuers rated Prime-1 have a superior capacity for repayment of
    short-term promissory obligations. Issuers rated Prime-2 have a strong
    capacity for repayment of short-term promissory obligations; and Issuers
    rated Prime-3 have an acceptable capacity for repayment of short-term
    promissory obligations. Issuers rated Not Prime do not fall within any
    of the Prime rating categories.
 
    STANDARD & POOR'S CORPORATION ("STANDARD & POOR'S")
 
                                  BOND RATINGS
 
    A Standard & Poor's bond rating is a current assessment of the
    creditworthiness of an obligor with respect to a specific obligation.
    This assessment may take into consideration obligors such as guarantors,
    insurers, or lessees.
 
        The ratings are based on current information furnished by the issuer
    or obtained by Standard & Poor's from other sources it considers
    reliable. The ratings are based, in varying degrees, on the following
    considerations: (1) likelihood of default-capacity and willingness of
    the obligor as to the timely payment of interest and repayment of
    principal in accordance with the terms of the obligation; (2) nature of
    and provisions of the obligation; and (3) protection afforded by, and
    relative position of, the obligation in the event of bankruptcy,
    reorganization or other arrangement under the laws of bankruptcy and
    other laws affecting creditors' rights.
 
        Standard & Poor's does not perform an audit in connection with any
    rating and may, on occasion, rely on unaudited financial information.
    The ratings may be changed, suspended or withdrawn as a result of
    changes in, or unavailability of, such information, or for other
    reasons.
 
<TABLE>
<S>        <C>
AAA        Debt rated AAA has the highest rating assigned by Standard & Poor's. Capacity to pay
           interest and repay principal is extremely strong.
AA         Debt rated AA has a very strong capacity to pay interest and repay principal and differs
           from the highest-rated issues only in small degree.
A          Debt rated A has a strong capacity to pay interest and repay principal although they are
           somewhat more susceptible to the adverse effects of changes in circumstances and
           economic conditions than debt in higher-rated categories.
BBB        Debt rated BBB is 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 for debt in higher-rated
           categories.
           Bonds rated AAA, AA, A and BBB are considered investment grade bonds.
BB         Debt rated BB has less near-term vulnerability to default than other speculative grade
           debt. However, it faces major ongoing uncertainties or exposure to adverse business,
           financial or economic conditions which could lead to inadequate capacity to meet timely
           interest and principal payment.
B          Debt rated B has a greater vulnerability to default but presently has the capacity to
           meet interest payments and principal repayments. Adverse business, financial or economic
           conditions would likely impair capacity or willingness to pay interest and repay
           principal.
CCC        Debt rated CCC has a current identifiable vulnerability to default, and is dependent
           upon favorable business, financial and economic conditions to meet timely payments of
           interest and repayments of principal. In the event of adverse business, financial or
           economic conditions, it is not likely to have the capacity to pay interest and repay
           principal.
CC         The rating CC is typically applied to debt subordinated to senior debt which is assigned
           an actual or implied CCC rating.
C          The rating C is typically applied to debt subordinated to senior debt which is assigned
           an actual or implied CCC- debt rating.
CI         The rating CI is reserved for income bonds on which no interest is being paid.
NR         Indicates that no rating has been requested, that there is insufficient information on
           which to base a rating or that Standard & Poor's does not rate a particular type of
           obligation as a matter of policy.
</TABLE>
 
28
<PAGE>
<TABLE>
<S>        <C>
           Bonds rated BB, B, CCC, CC and C are regarded as having predominantly speculative
           characteristics with respect to capacity to pay interest and repay principal. BB
           indicates the least degree of speculation and C the highest degree of speculation. While
           such debt will likely have some quality and protective characteristics, these are
           outweighed by large uncertainties or major risk exposures to adverse conditions.
           Plus (+) or minus (-): The ratings from AA to CCC may be modified by the addition of a
           plus or minus sign to show relative standing within the major ratings categories.
           In the case of municipal bonds, the foregoing ratings are sometimes followed by a "p"
           which indicates that the rating is provisional. A provisional rating assumes the
           successful completion of the project being financed by the bonds being rated and
           indicates that payment of debt service requirements is largely or entirely dependent
           upon the successful and timely completion of the project. This rating, however, while
           addressing credit quality subsequent to completion of the project, makes no comment on
           the likelihood or risk of default upon failure of such completion.
</TABLE>
 
                            COMMERCIAL PAPER RATINGS
 
    Standard and Poor's commercial paper rating is a current assessment of
    the likelihood of timely payment of debt having an original maturity of
    no more than 365 days. The commercial paper rating is not a
    recommendation to purchase or sell a security. The ratings are based
    upon current information furnished by the issuer or obtained by S&P from
    other sources it considers reliable. The ratings may be changed,
    suspended, or withdrawn as a result of changes in or unavailability of
    such information. Ratings are graded into group categories, ranging from
    "A" for the highest quality obligations to "D" for the lowest. Ratings
    are applicable to both taxable and tax-exempt commercial paper. The
    categories are as follows:
 
    Issues assigned A ratings are regarded as having the greatest capacity
    for timely payment. Issues in this category are further refined with the
    designation 1, 2 and 3 to indicate the relative degree of safety.
 
<TABLE>
<S>        <C>
    A-1 indicates that the degree of safety regarding timely payment is very strong.
    A-2 indicates capacity for timely payment on issues with this designation is strong. However,
        the relative degree of safety is not as overwhelming as for issues designated "A-1".
    A-3 indicates a satisfactory capacity for timely payment. Obligations carrying this designation
        are, however, somewhat more vulnerable to the adverse effects of changes in circumstances
        than obligations carrying the higher designations.
</TABLE>
 
                                                                              29
<PAGE>
MORGAN STANLEY DEAN WITTER
HIGH YIELD SECURITIES INC.
TWO WORLD TRADE CENTER
NEW YORK, NEW YORK 10048
 
BOARD OF DIRECTORS
Michael Bozic
Charles A. Fiumefreddo
Edwin J. Garn
John R. Haire
Wayne E. Hedien
Manuel H. Johnson
Michael E. Nugent
Philip J. Purcell
John L. Schroeder
 
OFFICERS
Charles A. Fiumefreddo
Chairman and Chief Executive Officer
Barry Fink
Vice President, Secretary and
General Counsel
Peter M. Avelar
Vice President
Thomas F. Caloia
Treasurer
 
CUSTODIAN
The Bank of New York
90 Washington Street
New York, New York 10286
 
TRANSFER AGENT AND
DIVIDEND DISBURSING AGENT
Morgan Stanley Dean Witter Trust FSB
Harborside Financial Center
Plaza Two
Jersey City, New Jersey 07311
 
INDEPENDENT ACCOUNTANTS
PricewaterhouseCoopers LLP
1177 Avenue of the Americas
New York, New York 10036
 
INVESTMENT MANAGER
Morgan Stanley Dean Witter Advisors Inc.


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