NML VARIABLE ANNUITY ACCOUNT A
497, 1999-05-17
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<PAGE>

April 30, 1999

NORTHWESTERN
MUTUAL LIFE-Registered Trademark-
The Quiet Company-Registered Trademark-

NML Variable Annuity Account A

Individual Variable Annuity Contracts for Retirement 
Plans of Self-Employed Persons and Their Employees




Northwestern Mutual
Series Fund, Inc. and
Russell Insurance Funds

The Northwestern Mutual 
Life Insurance Company
720 East Wisconsin Avenue
Milwaukee, WI  53202
(414) 271-1444



PROSPECTUSES
<PAGE>
 
                             The
      [LOGO]                 Northwestern
                PROFILE      Mutual Life
- ----------                   Insurance
                             Company
                             NML
                             Variable
                             Annuity
                             Account
                             A
 
                                                                  April 30, 1999
 
PROFILE OF THE VARIABLE ANNUITY CONTRACT
 
THIS PROFILE IS A SUMMARY OF SOME OF THE MORE IMPORTANT POINTS THAT YOU SHOULD
CONSIDER AND KNOW BEFORE PURCHASING THE CONTRACT. WE DESCRIBE THE CONTRACT MORE
FULLY IN THE PROSPECTUS WHICH ACCOMPANIES THIS PROFILE. PLEASE READ THE
PROSPECTUS CAREFULLY.
 
1.  THE ANNUITY CONTRACT  The Contract provides retirement annuity benefits for
self-employed individuals (and their eligible employees). The Contract will
invest on a tax-deferred basis in your choice of sixteen investment portfolios.
The Contract also allows investment on a fixed basis in a guaranteed account.
 
The Contract is intended for retirement savings or other long-term investment
purposes. The Contract provides for a death benefit during the years when funds
are being accumulated and for a variety of income options following retirement.
 
The sixteen investment portfolios are listed in Section 4 below. These
portfolios bear varying amounts of investment risk. Those with more risk are
designed to produce a better long-term return than those with less risk. But
this is not guaranteed. You can also lose your money.
 
The amounts invested on a fixed basis earn interest at a rate we set once each
year. Both interest and principal are guaranteed by Northwestern Mutual Life.
 
You may invest in any or all of the sixteen investment portfolios. You may move
money among these portfolios without charge up to 12 times per year. After that,
a charge of $25 may apply. Transfers of amounts invested on a fixed basis are
subject to restrictions.
 
During the years when funds are being paid into your Contract, known as the
accumulation phase, the earnings accumulate on a tax-deferred basis. The
earnings are taxed as income if you make a withdrawal. The income phase begins
when you start receiving annuity payments from your Contract, usually at
retirement. Monthly annuity payments begin on the date you select.
 
The amount you accumulate in your Contract, including the results of investment
performance, will determine the amount of your monthly annuity payments.
 
2.  ANNUITY PAYMENTS  If you decide to begin receiving monthly annuity payments
from your Contract, you may choose one of three payment plans: (1) monthly
payments for a specified period of five to thirty years, as you select; (2)
monthly payments for your life (assuming you are the annuitant), and you may
choose to have payments continue to your beneficiary for the balance of ten or
twenty years if you die sooner; or (3) monthly payments for your life and for
the life of another person (usually your spouse) selected by you. After you
begin receiving monthly annuity payments you cannot change your selection if the
payments depend on your life or the life of another.
 
These payment plans are available to you on a variable or fixed basis. Variable
means that the amount accumulated in your Contract will continue to be invested
in one or more of the sixteen investment portfolios as you choose. Your monthly
annuity payments will vary up or down to reflect continuing investment
performance. Or you may choose a fixed annuity payment plan which guarantees the
amount you will receive each month.
 
3.  PURCHASE  You may make purchase payments of $25 or more as you accumulate
funds in your Contract. The minimum initial purchase payment is $100, or $25 for
Contracts used with some tax-qualified retirement plans. We offer Front Load and
Back Load Contracts, as briefly described in Section 5. For the Front Load
Contract the minimum initial purchase payment is $10,000. Your Northwestern
Mutual Life agent will help you complete a Contract application form.
 
4.  INVESTMENT CHOICES  You may invest in any or all of the following investment
portfolios. All of these are described in the attached prospectuses for
Northwestern Mutual Series Fund, Inc. and the Russell Insurance Funds:
 
Northwestern Mutual Series Fund, Inc.
 
    1.  Small Cap Growth Stock Portfolio
    2.  Aggressive Growth Stock Portfolio
    3.  International Equity Portfolio
    4.  Index 400 Stock Portfolio
    5.  Growth Stock Portfolio
    6.  Growth and Income Stock Portfolio
    7.  Index 500 Stock Portfolio
    8.  Balanced Portfolio
    9.  High Yield Bond Portfolio
    10. Select Bond Portfolio
    11. Money Market Portfolio
 
                                    PROFILE
                                       --
                                       i
<PAGE>
 
                             The
      [LOGO]                 Northwestern
                PROFILE      Mutual Life
- ----------                   Insurance
                             Company
                             NML
                             Variable
                             Annuity
                             Account
                             A
 
                                                                  April 30, 1999
 
Russell Insurance Funds
 
    1.  Multi-Style Equity Fund
    2.  Aggressive Equity Fund
    3.  Non-U.S. Fund
    4.  Real Estate Securities Fund
    5.  Core Bond Fund
 
You may also invest all or part of your funds on a fixed basis (the Guaranteed
Interest Fund).
 
5.  EXPENSES  The Contract has insurance and investment features, and there are
costs related to them. For the Front Load Contract we deduct a sales load of 4%
from your purchase payments. The percentage is lower when cumulative purchase
payments exceed $100,000. For the Back Load Contract there is no sales load
deducted from purchase payments but a withdrawal charge of 0% to 8% applies,
depending on the length of time the money you withdraw has been in the Contract
and the size of your Contract.
 
Each year we deduct a $30 Contract fee. Currently this fee is waived if the
value of your Contract is $50,000 or more.
 
We also deduct mortality and expense risk charges for the guarantees associated
with your Contract. These charges are at the annual rate of .40% for the Front
Load Contract and 1.25% for the Back Load Contract.
 
The portfolios also bear investment charges that range from an annual rate of
 .21% to 1.30% of the average daily value of the portfolio, depending on the
investment portfolio you select. The following charts are designed to help you
understand the charges for the Front Load and Back Load Contracts. The first
three columns show the annual expenses as a percentage of assets including the
insurance charges, the portfolio charges and the total charges. Portfolio
expenses are based on 1998 expenses for the thirteen portfolios that were in
operation during 1998. Portfolio expenses for the other three portfolios, which
have not begun operations, are estimated for 1999 at an annualized rate.
Expenses for the portfolios reflect fee waivers and expense reimbursements. The
last two columns show you examples of the charges, in dollars, you would pay.
The examples reflect the impact of the asset based charges, any sales loads or
withdrawals that would apply, and the $30 Contract fee calculated by dividing
the annual Contract fees collected by the average assets of the sub-account. The
examples assume that you invested $1,000 in a Contract which earns 5% annually
and that you withdraw your money at the end of year one, and at the end of year
ten. Both of these examples, for both Contracts, reflect aggregate charges on a
cumulative basis to the end of the 1 or 10-year period.
For more detailed information, see the Expense Table which begins on page 3 of
the attached prospectus for the Contracts.
 
                                    EXPENSES
- --------------------------------------------------------------------------------
FRONT LOAD CONTRACT
                   ANNUAL EXPENSES AS A PERCENTAGE OF ASSETS
 
<TABLE>
<CAPTION>
                                                                                                     EXAMPLES: *
                                                                                                        Total Annual Charges At
                                                 Total Annual       Total Annual       Total Annual              End of
Portfolio                                      Insurance Charges  Portfolio Charges      Expenses         1 Year      10 Years
<S>                                            <C>                <C>                <C>                <C>          <C>
- -------------------------------------------------------------------------------------------------------------------------------
NORTHWESTERN MUTUAL SERIES FUND, INC.
  Small Cap Growth Stock                                .42%              1.00%              1.42%       $      54    $     203
  Aggressive Growth Stock                               .42                .52                .94        $      49    $     151
  International Equity                                  .42                .76               1.18        $      52    $     178
  Index 400 Stock                                       .42                .35                .77        $      48    $     132
  Growth Stock                                          .42                .46                .88        $      49    $     144
  Growth and Income Stock                               .42                .58               1.00        $      50    $     158
  Index 500 Stock                                       .42                .21                .63        $      46    $     116
  Balanced                                              .42                .30                .72        $      47    $     126
  High Yield Bond                                       .42                .50                .92        $      49    $     149
  Select Bond                                           .42                .30                .72        $      47    $     126
  Money Market                                          .42                .30                .72        $      47    $     126
RUSSELL INSURANCE FUNDS
  Multi-Style Equity                                    .42                .92               1.34        $      53    $     195
  Aggressive Equity                                     .42               1.25               1.67        $      56    $     230
  Non-U.S.                                              .42               1.30               1.72        $      57    $     235
  Real Estate Securities                                .42               1.15               1.57        $      55    $     219
  Core Bond                                             .42                .80               1.22        $      52    $     182
</TABLE>
 
NOTE: THE MINIMUM INITIAL PURCHASE PAYMENT FOR A FRONT LOAD CONTRACT IS $10,000.
THE NUMBERS ABOVE MUST BE MULTIPLIED BY 10 TO FIND THE EXPENSES FOR A FRONT LOAD
CONTRACT OF MINIMUM SIZE.
*   THE $30 CONTRACT FEE IS REFLECTED AS .02% OF THE ASSETS BASED ON ACTUAL FEES
    COLLECTED DIVIDED BY AVERAGE ASSETS OF THE SUB-ACCOUNT.
 
                                    PROFILE
                                       --
                                       ii
<PAGE>
 
                             The
      [LOGO]                 Northwestern
                PROFILE      Mutual Life
- ----------                   Insurance
                             Company
                             NML
                             Variable
                             Annuity
                             Account
                             A
 
                                                                  April 30, 1999
 
BACK LOAD CONTRACT
                   ANNUAL EXPENSES AS A PERCENTAGE OF ASSETS
 
<TABLE>
<CAPTION>
                                                                                                    EXAMPLES: **
                                                                                                        Total Annual Charges At
                                                 Total Annual       Total Annual       Total Annual              End of
Portfolio                                      Insurance Charges  Portfolio Charges      Expenses         1 Year      10 Years
<S>                                            <C>                <C>                <C>                <C>          <C>
- -------------------------------------------------------------------------------------------------------------------------------
NORTHWESTERN MUTUAL SERIES FUND, INC.
  Small Cap Growth Stock                               1.51%              1.00%              2.51%       $     105    $     285
  Aggressive Growth Stock                              1.51                .52               2.03        $     101    $     237
  International Equity                                 1.51                .76               2.27        $     103    $     261
  Index 400 Stock                                      1.51                .35               1.86        $      96    $     216
  Growth Stock                                         1.51                .46               1.97        $     100    $     230
  Growth and Income Stock                              1.51                .58               2.09        $     101    $     243
  Index 500 Stock                                      1.51                .21               1.72        $      98    $     204
  Balanced                                             1.51                .30               1.81        $      98    $     213
  High Yield Bond                                      1.51                .50               2.01        $     100    $     234
  Select Bond                                          1.51                .30               1.81        $      98    $     213
  Money Market                                         1.51                .30               1.81        $      98    $     213
RUSSELL INSURANCE FUNDS
  Multi-Style Equity                                   1.51                .92               2.43        $     105    $     277
  Aggressive Equity                                    1.51               1.25               2.76        $     108    $     310
  Non-U.S.                                             1.51               1.30               2.81        $     108    $     314
  Real Estate Securities                               1.51               1.15               2.66        $     107    $     300
  Core Bond                                            1.51                .80               2.31        $     103    $     265
</TABLE>
 
**  THE $30 CONTRACT FEE IS REFLECTED AS 0.26% OF THE ASSETS BASED ON ACTUAL
    FEES COLLECTED DIVIDED BY AVERAGE ASSETS OF THE SUB-ACCOUNT.
 
6.  TAXES  As a general rule, earnings on your Contract are not taxed until they
are withdrawn or taken as monthly annuity payments. A 10% federal tax penalty
may apply if you make withdrawals from the Contract before you reach age 59 1/2.
 
7.  ACCESS TO YOUR MONEY  You may take money out of your Contract at any time
before monthly annuity payments begin. For the Front Load Contract there is no
charge for withdrawals. For the Back Load Contract there is a withdrawal charge
of 8% or less, depending on how much money has been paid into the Contract and
how long it has been held there. Each purchase payment has its own withdrawal
charge period. When you make a withdrawal, we use the oldest amounts first when
the charge is calculated. After the first year, part of any investment earnings
may be withdrawn without a withdrawal charge.
 
For both Front Load and Back Load Contracts, you may also have to pay income tax
and a tax penalty on amounts you take out.
 
8.  PERFORMANCE  The value of your Contract will vary up or down reflecting the
performance of the investment portfolios you select. The chart below shows total
returns for each of the investment portfolios that was in operation, and used
with the Account, during the years shown. These numbers, for the Front Load
Contract and the Back Load Contract, reflect the asset-based charges for
mortality and expense risks, the annual Contract fees and investment expenses
for each portfolio. The numbers include the annual Contract fee in the amount of
 .02% for the Front Load Contract and .26% for the Back Load Contract. The
numbers do not reflect deductions from purchase payments for the Front Load
Contract or any withdrawal charge for the Back Load Contract. Those charges, if
applied, would reduce the performance. Past performance does not guarantee
future results.
 
                                    PROFILE
                                       --
                                      iii
<PAGE>
 
                             The
      [LOGO]                 Northwestern
                PROFILE      Mutual Life
- ----------                   Insurance
                             Company
                             NML
                             Variable
                             Annuity
                             Account
                             A
 
                                                                  April 30, 1999
 
                                  PERFORMANCE
- --------------------------------------------------------------------------------
FRONT LOAD CONTRACT
 
<TABLE>
<CAPTION>
                                                               Calendar Year
Portfolio                            1998   1997   1996   1995   1994   1993   1992  1991   1990  1989
<S>                                  <C>    <C>    <C>    <C>    <C>    <C>    <C>   <C>    <C>   <C>
- -------------------------------------------------------------------------------------------------------
Aggressive Growth Stock               7.10  13.39  17.20  38.71   4.96  18.61  5.50  55.07   NA      NA
International Equity                  4.38  11.81  20.50  14.09   -.52     NA   NA      NA   NA      NA
Growth Stock                         26.16  29.31  20.40  30.27     NA     NA   NA      NA   NA      NA
Growth and Income Stock              22.62  29.48  19.46  30.57     NA     NA   NA      NA   NA      NA
Index 500 Stock                      28.18  32.64  22.23  36.68    .77   9.31  6.81  29.02   NA      NA
Balanced                             18.38  21.01  12.97  25.86   -.44   9.12  4.88  23.42  .62   15.12
High Yield Bond                      -2.26  15.36  19.26  16.29     NA     NA   NA      NA   NA      NA
Select Bond                           6.62   9.00   2.88  18.60  -3.24   9.87  6.54  16.39  7.87  13.39
Money Market                          4.98   5.03   4.84   5.38   3.62   2.42  2.91   5.25  7.58   8.52
</TABLE>
 
BACK LOAD CONTRACT
 
<TABLE>
<CAPTION>
                                                               Calendar Year
Portfolio                            1998   1997   1996   1995   1994   1993   1992  1991   1990  1989
<S>                                  <C>    <C>    <C>    <C>    <C>    <C>    <C>   <C>    <C>   <C>
- -------------------------------------------------------------------------------------------------------
Aggressive Growth Stock               5.95  12.16  15.93  37.21   3.83  17.33  4.36  53.66    NA     NA
International Equity                  3.25  10.60  19.19  12.86  -1.59     NA   NA      NA    NA     NA
Growth Stock                         24.79  27.91  19.09  28.87     NA     NA   NA      NA    NA     NA
Growth and Income Stock              21.29  28.08  18.16  29.16     NA     NA   NA      NA    NA     NA
Index 500 Stock                      26.80  31.21  20.90  35.20   -.32   8.13  5.65  27.61    NA     NA
Balanced                             17.10  19.70  11.74  24.50  -1.51   7.94  3.74  22.08  -.49  13.87
High Yield Bond                      -3.31  14.12  17.97  15.03     NA     NA   NA      NA    NA     NA
Select Bond                           5.47   7.83   1.76  17.32  -4.29   8.68  5.38  15.13  6.70  12.17
Money Market                          3.85   3.89   3.70   4.24   2.50   1.31  1.79   4.11  6.41   7.35
</TABLE>
 
9.  DEATH BENEFIT  If you die before age 65, and before monthly annuity payments
begin, your beneficiary will receive a death benefit. The amount will be the
value of your Contract or, if greater, the amount you have paid in. The death
benefit will be adjusted, of course, for any withdrawals you have made. The
death benefit will be paid as a lump sum or your beneficiary may select a
monthly annuity payment plan.
 
10.  OTHER INFORMATION
 
FREE LOOK.  If you return the Contract within ten days after you receive it (or
whatever period is required in your state), we will send your money back. There
is no charge for our expenses but the amount you receive may be more or less
than what you paid, based on actual investment experience following the date we
received your purchase payment.
 
AVOID PROBATE.  In most cases, when you die, your beneficiary will receive the
full death benefit of your Contract without going through probate.
 
AUTOMATIC DOLLAR-COST AVERAGING.  With our Dollar-Cost Averaging Plan, you can
arrange to have a regular amount of money ($100 minimum) automatically
transferred from the Money Market Portfolio into the portfolio or portfolios you
have chosen on a monthly or quarterly basis.
 
ELECTRONIC FUNDS TRANSFER (EFT).  Another convenient way to invest using the
dollar-cost averaging approach is through our EFT Plan. These automatic
checkbook withdrawals allow you to add to your portfolio(s) on a regular monthly
basis through payments drawn directly on your checking account.
 
SYSTEMATIC WITHDRAWAL PLAN.  You can arrange to have regular amounts of money
sent to you while your Contract is still in the accumulation phase. Our
Systematic Withdrawal Plan allows you to automatically redeem accumulation units
to generate monthly payments. Of course you will have to pay taxes on certain
amounts of money you receive.
 
                                    PROFILE
                                       --
                                       iv
<PAGE>
 
                             The
      [LOGO]                 Northwestern
                PROFILE      Mutual Life
- ----------                   Insurance
                             Company
                             NML
                             Variable
                             Annuity
                             Account
                             A
 
                                                                  April 30, 1999
 
AUTOMATIC REQUIRED MINIMUM DISTRIBUTIONS.  You can arrange for annual required
minimum distributions to be sent to you automatically once you turn age 70 1/2.
 
DIVIDENDS.  We are paying dividends on approximately 18% of our inforce variable
annuity contracts in 1999, primarily older, larger contracts. The dividends
arise principally as a result of more favorable expense results than assumed in
determining deductions on these contracts.
 
PORTFOLIO REBALANCING.  To help you maintain your asset allocation plan over
time we offer a rebalancing service. This will automatically readjust your
investment option allocations, on a periodic basis, back to the allocation
percentages you have selected.
 
INTEREST SWEEPS.  If you select this service we will automatically sweep or
transfer interest from the Guaranteed Interest Fund to any combination of
variable investment options. Interest earnings can be swept monthly, quarterly,
semi-annually or annually.
 
NML EXPRESS. 1-800-519-4NML (1-800-519-4665).  Get up-to-date information about
your contract at your convenience with your contract number and your Personal
Identification Number (PIN). Call toll-free to review contract values and unit
values, transfer among portfolios, change the allocation and obtain fund
performance information.
 
INTERNET.  For information about Northwestern Mutual Life, visit us on our
Website. Included are daily unit values and fund performance information.
 
                           WWW.NORTHWESTERNMUTUAL.COM
 
11.  INQUIRIES  If you need more information, please contact us at:
 
THE NORTHWESTERN MUTUAL LIFE INSURANCE COMPANY, 720 EAST WISCONSIN AVENUE,
MILWAUKEE, WISCONSIN 53202; (414) 271-1444
 
                                    PROFILE
                                       --
                                       v
<PAGE>
                 (This page has been left blank intentionally.)
<PAGE>
PROSPECTUS
 
NML VARIABLE ANNUITY ACCOUNT A
 
This prospectus describes individual variable annuity contracts (the
"Contracts") offered by The Northwestern Mutual Life Insurance Company
("Northwestern Mutual Life") to provide retirement annuity benefits for
self-employed individuals (and their eligible employees) who adopt plans meeting
the requirements of Sections 401 or 403(a) of the Internal Revenue Code of 1986,
as amended. These plans, popularly called HR-10 Plans, afford certain federal
income tax benefits to employers and to employees and their beneficiaries.
 
We use NML Variable Annuity Account A (the "Account") to keep the money you
invest separate from our general assets. The money in the Account is invested in
the eleven portfolios of Northwestern Mutual Series Fund, Inc. and the five
Russell Insurance Funds. You select the Portfolios or Funds in which you want to
invest. The Account has 16 Divisions that correspond to the 11 Portfolios and 5
Funds in which you may invest. The Contracts also permit you to invest on a
fixed basis, at rates that we determine. This prospectus describes only the
Account and the variable provisions of the Contracts except where there are
specific references to the fixed provisions.
 
We offer two versions of the Contracts: Front Load Contracts and Back Load
Contracts. See the Expense table on page 3 and the Deductions section, beginning
on page 16.
 
This prospectus is a concise description of the information you should know
before you buy a Contract. We have filed additional information about the
Contracts with the Securities and Exchange Commission in a Statement of
Additional Information. We incorporate the Statement of Additional Information
into this prospectus by reference. We will send you the Statement of Additional
Information without charge if you write to The Northwestern Mutual Life
Insurance Company, 720 East Wisconsin Avenue, Milwaukee, Wisconsin, 53202, or
call us at Telephone Number (414) 271-1444. You will find the table of contents
for the Statement of Additional Information following page 19 of this
prospectus.
 
This prospectus is valid only when accompanied by the current prospectuses for
Northwestern Mutual Series Fund, Inc. and the Russell Insurance Funds which are
attached to this prospectus. You should retain this prospectus for future
reference.
 
The Securities and Exchange Commission has not approved or disapproved these
securities or passed upon the adequacy of this prospectus. Any representation to
the contrary is a criminal offense.
 
The Date of this prospectus and the Statement of Additional Information is April
30, 1999.
 
                                       --
                                       1
<PAGE>
CONTENTS FOR THIS PROSPECTUS
<TABLE>
<CAPTION>
                                                           Page
                                                           -----
<S>                                                     <C>
PROFILE...............................................         i-v
 
PROSPECTUS............................................           1
 
  NML Variable Annuity Account A......................           1
 
INDEX OF SPECIAL TERMS................................           3
 
EXPENSE TABLE.........................................           3
 
ACCUMULATION UNIT VALUES..............................           6
 
THE COMPANY...........................................           9
 
NML VARIABLE ANNUITY ACCOUNT A........................           9
 
THE FUNDS.............................................           9
 
THE CONTRACTS.........................................          10
 
  Purchase Payments Under the Contracts...............          10
 
    Amount and Frequency..............................          10
 
    Application of Purchase Payments..................          10
 
  Net Investment Factor...............................          10
 
  Benefits Provided Under the Contracts...............          11
 
    Withdrawal Amount.................................          11
 
    Death Benefit.....................................          11
 
    Maturity Benefit..................................          11
 
  Variable Payment Plans..............................          12
 
    Description of Payment Plans......................          12
 
    Amount of Annuity Payments........................          12
 
<CAPTION>
                                                           Page
                                                           -----
<S>                                                     <C>
 
    Assumed Investment Rate...........................          12
 
  Additional Information..............................          12
 
    Transfers Between Divisions and Payment Plans.....          12
 
    Gender-Based Annuity Payment Rates................          13
 
    Owners of the Contracts...........................          13
 
    Deferment of Benefit Payments.....................          13
 
    Dividends.........................................          14
 
    Substitution and Change...........................          14
 
    Fixed Annuity Payment Plans.......................          14
 
    Financial Statements..............................          14
 
THE GUARANTEED INTEREST FUND..........................          14
 
FEDERAL INCOME TAXES..................................          15
 
  Contribution Limits.................................          15
 
  Taxation of Contract Benefits.......................          15
 
  Taxation of Northwestern Mutual Life................          16
 
DEDUCTIONS............................................          16
 
  Contracts Issued Prior to March 31, 1995............          18
 
  Contracts Issued Prior to December 17, 1981.........          18
 
  Reduced Charges for Exchange Transactions...........          18
 
DISTRIBUTION OF THE CONTRACTS.........................          19
 
YEAR 2000 ISSUES......................................          19
</TABLE>
 
THE TABLE OF CONTENTS FOR THE STATEMENT OF ADDITIONAL INFORMATION APPEARS ON THE
                   PAGE FOLLOWING PAGE 19 OF THIS PROSPECTUS.
 
                                       --
                                       2
<PAGE>
INDEX OF SPECIAL TERMS
 
THE FOLLOWING SPECIAL TERMS USED IN THIS PROSPECTUS ARE DISCUSSED AT THE PAGES
INDICATED.
<TABLE>
<CAPTION>
TERM                                                       PAGE
- ------------------------------------------------------     -----
<S>                                                     <C>
Accumulation Unit.....................................          10
Annuity (or Annuity Payments).........................          12
Net Investment Factor.................................          10
Payment Plans.........................................          12
 
<CAPTION>
TERM                                                       PAGE
- ------------------------------------------------------     -----
<S>                                                     <C>
Annuitant.............................................          13
Maturity Date.........................................          11
Owner.................................................          13
Withdrawal Amount.....................................          11
</TABLE>
 
- --------------------------------------------------------------------------------
EXPENSE TABLE
 
<TABLE>
<S>                                              <C>
FRONT LOAD CONTRACT
TRANSACTION EXPENSES FOR CONTRACTOWNERS
Maximum Sales Load (as a percentage of purchase
payments)......................................         4%
Withdrawal Charge..............................       None
ANNUAL EXPENSES OF THE ACCOUNT
(AS A PERCENTAGE OF ASSETS)
Mortality and Expense Risk Fees................       .40%
Total Separate Account Annual Expenses.........       .40%
 
ANNUAL CONTRACT FEE
$30; waived if the Contract Value equals or
exceeds $50,000
</TABLE>
 
    ------------------------------------------------------------------------
 
<TABLE>
<S>                                             <C>
BACK LOAD CONTRACT
TRANSACTION EXPENSES FOR CONTRACTOWNERS
Sales Load (as a percentage of purchase
payments).....................................       None
Withdrawal Charge for Sales Expenses
(as a percentage of amounts paid).............      0%-8%
 
ANNUAL EXPENSES OF THE ACCOUNT
(AS A PERCENTAGE OF ASSETS)
Mortality and Expense Risk Fees...............      1.25%
Total Separate Account Annual Expenses........      1.25%
 
ANNUAL CONTRACT FEE AND FUNDS
$30; waived if the Contract Value equals or
exceeds $50,000
</TABLE>
 
ANNUAL EXPENSES OF THE PORTFOLIOS AND FUNDS
(AS A PERCENTAGE OF THE ASSETS)
 
<TABLE>
<CAPTION>
                                                                                                                 TOTAL ANNUAL
                                                                                                                   EXPENSES
                                                                    MANAGEMENT FEES                             (AFTER EXPENSE
                                                                  (AFTER FEE WAIVER)       OTHER EXPENSES       REIMBURSEMENT)
                                                                -----------------------  -------------------  -------------------
<S>                                                             <C>                      <C>                  <C>
NORTHWESTERN MUTUAL SERIES FUND, INC.
  Small Cap Growth Stock*.....................................              .80%                   .20%                1.00%
  Aggressive Growth Stock.....................................              .52%                   .00%                 .52%
  International Equity........................................              .67%                   .09%                 .76%
  Index 400 Stock*............................................              .25%                   .10%                 .35%
  Growth Stock................................................              .45%                   .01%                 .46%
  Growth and Income Stock.....................................              .57%                   .01%                 .58%
  Index 500 Stock.............................................              .20%                   .01%                 .21%
  Balanced....................................................              .30%                   .00%                 .30%
  High Yield Bond.............................................              .49%                   .01%                 .50%
  Select Bond.................................................              .30%                   .00%                 .30%
  Money Market................................................              .30%                   .00%                 .30%
RUSSELL INSURANCE FUNDS**
  Multi-Style Equity..........................................              .49%                   .43%                 .92%
  Aggressive Equity...........................................              .53%                   .72%                1.25%
  Non-U.S.....................................................              .00%                  1.30%                1.30%
  Real Estate Securities*.....................................              .85%                   .30%                1.15%
  Core Bond...................................................              .12%                   .68%                 .80%
</TABLE>
 
* Expenses are estimated for these new Portfolios and Funds, for 1999 at
annualized rates.
** For the Russell Insurance Funds, the adviser has voluntarily agreed to waive
a portion of the management fee, up to the full amount of the fee, equal to the
amount by which the Fund's total operating expenses exceed the amounts shown
above under "Total Annual Expenses (After Expense Reimbursement)". The adviser
has also agreed to reimburse the Fund for all remaining expenses after fee
waivers which exceed the amounts shown above under that heading. Absent the fee
waiver and expense reimbursement, the management fees and total annual expenses
would be .78% and 1.21% for the Multi-Style Equity Fund; .95% and 1.67% for the
Aggressive Equity Fund; .95% and 2.37% for the Non-U.S. Fund; .85% and 1.15% for
the Real Estate Securities Fund; and .60% and 1.28% for the Core Bond Fund.
 
                                       --
                                       3
<PAGE>
- --------------------------------------------------------------------------------
 
EXAMPLE
 
FRONT LOAD CONTRACT -- You would pay the following expenses on each $1,000
investment, assuming 5% annual return:
 
<TABLE>
<CAPTION>
                                                          1 YEAR       3 YEARS      5 YEARS     10 YEARS
                                                        -----------  -----------  -----------  -----------
<S>                                                     <C>          <C>          <C>          <C>
NORTHWESTERN MUTUAL SERIES FUND, INC.
  Small Cap Growth Stock..............................   $      54    $      83    $     115    $     203
  Aggressive Growth Stock.............................   $      49    $      69    $      90    $     151
  International Equity................................   $      52    $      76    $     102    $     178
  Index 400 Stock.....................................   $      48    $      64    $      81    $     132
  Growth Stock........................................   $      49    $      67    $      87    $     144
  Growth and Income Stock.............................   $      50    $      71    $      93    $     158
  Index 500 Stock.....................................   $      46    $      59    $      74    $     116
  Balanced............................................   $      47    $      62    $      78    $     126
  High Yield Bond.....................................   $      49    $      68    $      89    $     149
  Select Bond.........................................   $      47    $      62    $      78    $     126
  Money Market........................................   $      47    $      62    $      78    $     126
RUSSELL INSURANCE FUNDS
  Multi-Style Equity..................................   $      53    $      81    $     111    $     195
  Aggressive Equity...................................   $      56    $      91    $     127    $     230
  Non-U.S.............................................   $      57    $      92    $     130    $     235
  Real Estate Securities..............................   $      55    $      88    $     122    $     219
  Core Bond...........................................   $      52    $      77    $     104    $     182
</TABLE>
 
NOTE: THE MINIMUM INITIAL PURCHASE PAYMENT FOR A FRONT-LOAD CONTRACT IS $10,000.
YOU MUST MULTIPLY THE NUMBERS ABOVE BY 10 TO FIND THE EXPENSES FOR A FRONT-LOAD
CONTRACT OF MINIMUM SIZE.
 
EXAMPLE
 
BACK LOAD CONTRACT -- You would pay the following expenses on a $1,000
investment, assuming (1) 5% annual return and (2) surrender just prior to the
end of each time period:
 
<TABLE>
<CAPTION>
                                                          1 YEAR       3 YEARS      5 YEARS     10 YEARS
                                                        -----------  -----------  -----------  -----------
<S>                                                     <C>          <C>          <C>          <C>
NORTHWESTERN MUTUAL SERIES FUND, INC.
  Small Cap Growth Stock..............................   $     105    $     138    $     174    $     285
  Aggressive Growth Stock.............................   $     101    $     124    $     150    $     237
  International Equity................................   $     103    $     131    $     162    $     261
  Index 400 Stock.....................................   $      96    $     116    $     138    $     216
  Growth Stock........................................   $     100    $     122    $     147    $     230
  Growth and Income Stock.............................   $     101    $     126    $     153    $     243
  Index 500 Stock.....................................   $      98    $     114    $     134    $     204
  Balanced............................................   $      98    $     117    $     138    $     213
  High Yield Bond.....................................   $     100    $     123    $     149    $     234
  Select Bond.........................................   $      98    $     117    $     138    $     213
  Money Market........................................   $      98    $     117    $     138    $     213
RUSSELL INSURANCE FUNDS
  Multi-Style Equity..................................   $     105    $     136    $     170    $     277
  Aggressive Equity...................................   $     108    $     146    $     186    $     310
  Non-U.S.............................................   $     108    $     147    $     189    $     314
  Real Estate Securities..............................   $     107    $     143    $     181    $     300
  Core Bond...........................................   $     103    $     132    $     164    $     265
</TABLE>
 
                                       --
                                       4
<PAGE>
You would pay the following expenses on the same $1,000 investment, assuming NO
SURRENDER OR ANNUITIZATION:
 
<TABLE>
<CAPTION>
                                                          1 YEAR       3 YEARS      5 YEARS     10 YEARS
                                                        -----------  -----------  -----------  -----------
<S>                                                     <C>          <C>          <C>          <C>
NORTHWESTERN MUTUAL SERIES FUND, INC.
  Small Cap Growth Stock                                 $      25    $      78    $     134    $     285
  Aggressive Growth Stock                                $      21    $      64    $     110    $     237
  International Equity                                   $      23    $      71    $     122    $     261
  Index 400 Stock                                        $      16    $      56    $      98    $     216
  Growth Stock                                           $      20    $      62    $     107    $     230
  Growth and Income Stock                                $      21    $      66    $     113    $     243
  Index 500 Stock                                        $      18    $      54    $      94    $     204
  Balanced                                               $      18    $      57    $      98    $     213
  High Yield Bond                                        $      20    $      63    $     109    $     234
  Select Bond                                            $      18    $      57    $      98    $     213
  Money Market                                           $      18    $      57    $      98    $     213
RUSSELL INSURANCE FUNDS
  Multi-Style Equity                                     $      25    $      76    $     130    $     277
  Aggressive Equity                                      $      28    $      86    $     146    $     310
  Non-U.S.                                               $      28    $      87    $     149    $     314
  Real Estate Securities                                 $      27    $      83    $     141    $     300
  Core Bond                                              $      23    $      72    $     124    $     265
</TABLE>
 
The purpose of the table above is to assist a Contract Owner in understanding
the expenses paid by the Account and the Portfolios and Funds and borne by
investors in the Contracts. The sales load for a Front Load Contract depends on
the amount of cumulative purchase payments. For the Back Load Contract the
withdrawal charge depends on the length of time funds have been held under the
Contract and the amounts held. The $30 annual Contract fee is reflected as .02%
for the Front Load Contract and .26% for the Back Load Contract based on the
annual Contract fees collected divided by the average assets of the sub-account.
The Contracts provide for charges for transfers between the Divisions of the
Account and for premium taxes, but we are not currently making such charges. See
"Transfers Between Divisions and Payment Plans", p. 12 and "Deductions", p. 16,
for additional information about expenses for the Contracts. The expenses shown
in the table for the Portfolios and Funds show the annual expenses for each, as
a percentage of their average net assets, based on 1998 operations for the
Portfolios and their predecessors and the Funds. Expenses for Portfolios and
Funds which have not begun operations are estimated. Expenses for each of the
Russell Insurance Funds reflect fee waivers and expense reimbursements that the
Funds' adviser has voluntarily agreed to make for 1999. These may be changed at
any time without notice. Absent the fee waivers and expense reimbursements the
expenses would be higher. See the disclosure at the bottom of page 3. For
additional information about expenses of the Portfolios and Funds, see the
prospectuses for Northwestern Mutual Series Fund, Inc. and the Russell Insurance
Funds attached to this prospectus.
 
The example should not be considered a representation of past or future
expenses. Actual expenses may be greater or less than those shown, subject to
the guarantees of the Contracts.
 
The tables on the following pages present the accumulation unit values of nine
Divisions of the Account for the Contracts, including Contracts issued prior to
the date of this prospectus. These nine Divisions are those which were in
operation in 1998 and prior years. The Contracts issued prior to March 31, 1995
are different in certain material respects from Contracts offered currently, but
the values shown below for Contracts issued after December 16, 1981 and prior to
March 31, 1995 are calculated on the same basis as those for the Back Load
Contracts described in this prospectus. The Front Load Contracts described in
this prospectus have a lower mortality rate and expense guarantee charge than
any of the Contracts issued prior to March 31, 1995.
 
                                       --
                                       5
<PAGE>
ACCUMULATION UNIT VALUES
 
CONTRACTS ISSUED ON OR AFTER MARCH 31, 1995
<TABLE>
<CAPTION>
                                             FOR YEARS ENDED          FOR THE NINE
                                               DECEMBER 31            MONTHS ENDED
                                     -------------------------------  DECEMBER 31,
                                       1998       1997       1996         1995
<S>                                  <C>        <C>        <C>        <C>
- ----------------------------------------------------------------------------------
AGGRESSIVE GROWTH STOCK DIVISION
Front Load Version
  Beginning of Period..............     $1.735     $1.530     $1.305       $1.00
  End of Period....................     $1.859     $1.735     $1.530      $1.305
Back Load Version
  Beginning of Period..............     $3.585     $3.188     $2.743      $2.115
  End of Period....................     $3.808     $3.585     $3.188      $2.743
 
Number of Units Outstanding, End of
 Period
  Front Load.......................  1,195,051    832,513    568,732     255,895
  Back Load........................  3,703,653  2,962,218  1,734,023     407,729
 
INTERNATIONAL EQUITY DIVISION
Front Load Version
  Beginning of Period..............     $1.537     $1.374     $1.140       $1.00
  End of Period....................     $1.605     $1.537     $1.374      $1.140
Back Load Version
  Beginning of Period..............     $1.829     $1.649     $1.380      $1.218
  End of Period....................     $1.893     $1.829     $1.649      $1.380
 
Number of Units Outstanding, End of
 Period
  Front Load.......................    669,024    575,775    286,469      32,573
  Back Load........................  3,028,502  2,488,184  1,281,128     374,986
 
GROWTH STOCK DIVISION
Front Load Version
  Beginning of Period..............     $1.883     $1.456     $1.209       $1.00
  End of Period....................     $2.375     $1.883     $1.456      $1.209
Back Load Version
  Beginning of Period..............     $1.991     $1.552     $1.300      $1.082
  End of Period....................     $2.491     $1.991     $1.552      $1.300
 
Number of Units Outstanding, End of
 Period
  Front Load.......................    447,934    422,029    257,158     103,292
  Back Load........................  2,761,432  1,870,296    922,390     227,218
 
GROWTH AND INCOME STOCK DIVISION
Front Load Version
  Beginning of Period..............     $1.852     $1.430     $1.197       $1.00
  End of Period....................     $2.271     $1.852     $1.430      $1.197
Back Load Version
  Beginning of Period..............     $1.959     $1.525     $1.287      $1.083
  End of Period....................     $2.382     $1.959     $1.525      $1.287
 
Number of Units Outstanding, End of
 Period
  Front Load.......................    736,836    540,977    208,323     114,414
  Back Load........................  3,046,517  1,940,827  1,215,721     310,321
 
INDEX 500 STOCK DIVISION
Front Load Version
  Beginning of Period..............     $2.026     $1.527     $1.249       $1.00
  End of Period....................     $2.597     $2.026     $1.527      $1.249
Back Load Version
  Beginning of Period..............     $3.175     $2.414     $1.991      $1.604
  End of Period....................     $4.037     $3.175     $2.414      $1.991
 
Number of Units Outstanding, End of
 Period
  Front Load.......................  1,057,935    690,248    454,096     278,235
  Back Load........................  4,504,322  3,279,176  1,970,961     471,752
 
<CAPTION>
                                             FOR YEARS ENDED          FOR THE NINE
                                               DECEMBER 31            MONTHS ENDED
                                     -------------------------------  DECEMBER 31,
                                       1998       1997       1996         1995
<S>                                  <C>        <C>        <C>        <C>
- ----------------------------------------------------------------------------------
 
BALANCED DIVISION
Front Load Version
  Beginning of Period..............     $1.615     $1.334     $1.181       $1.00
  End of Period....................     $1.912     $1.615     $1.334      $1.181
Back Load Version
  Beginning of Period..............     $5.768     $4.806     $4.290      $3.655
  End of Period....................     $6.771     $5.768     $4.806      $4.290
 
Number of Units Outstanding, End of
 Period
  Front Load.......................  1,768,955  1,296,330    786,271     164,302
  Back Load........................  2,565,265  2,109,606  1,347,427     372,457
 
HIGH YIELD BOND DIVISION
Front Load Version
  Beginning of Period..............     $1.530     $1.326     $1.112       $1.00
  End of Period....................     $1.496     $1.530     $1.326      $1.112
Back Load Version
  Beginning of Period..............     $1.595     $1.394     $1.178      $1.067
  End of Period....................     $1.546     $1.595     $1.394      $1.178
 
Number of Units Outstanding, End of
 Period
  Front Load.......................    400,132     95,718     55,625      --
  Back Load........................  1,400,604    967,118    572,121     138,470
 
SELECT BOND DIVISION
Front Load Version
  Beginning of Period..............     $1.266     $1.161     $1.129       $1.00
  End of Period....................     $1.350     $1.266     $1.161      $1.129
Back Load Version
  Beginning of Period..............     $6.703     $6.201     $6.078      $5.419
  End of Period....................     $7.088     $6.703     $6.201      $6.078
 
Number of Units Outstanding, End of
 Period
  Front Load.......................    159,609     72,941     38,713      26,732
  Back Load........................    368,314    271,027    182,907      50,828
 
MONEY MARKET DIVISION
Front Load Version
  Beginning of Period..............     $1.146     $1.091     $1.040       $1.00
  End of Period....................     $1.203     $1.146     $1.091      $1.040
Back Load Version
  Beginning of Period..............     $2.335     $2.241     $2.156      $2.086
  End of Period....................     $2.431     $2.335     $2.241      $2.156
 
Number of Units Outstanding, End of
 Period
  Front Load.......................  1,564,597  1,439,686  1,843,605     327,441
  Back Load........................  1,515,128  1,081,227  1,123,081     379,473
</TABLE>
 
                                       --
                                       6
<PAGE>
ACCUMULATION UNIT VALUES
 
CONTRACTS ISSUED AFTER DECEMBER 16, 1981 AND PRIOR TO MARCH 31, 1995
<TABLE>
<CAPTION>
                                                              FOR THE YEARS ENDED DECEMBER 31
                           ------------------------------------------------------------------------------------------------------
                               1998           1997           1996           1995           1994           1993           1992
                           ------------   ------------   ------------   ------------   ------------   ------------   ------------
<S>                        <C>            <C>            <C>            <C>            <C>            <C>            <C>
AGGRESSIVE GROWTH STOCK
  DIVISION
  Beginning of Period*           $3.585         $3.188         $2.743         $1.994         $1.915         $1.628         $1.556
  End of Period                  $3.808         $3.585         $3.188         $2.743         $1.994         $1.915         $1.628
  Number of Units
  Outstanding, End of
   Period                    18,213,135     20,861,309     21,479,837     19,083,707     17,290,856     11,319,698      7,939,571
 
INTERNATIONAL EQUITY
  DIVISION
  Beginning of Period**          $1.829         $1.649         $1.380         $1.220         $1.236         $1.000             --
  End of Period                  $1.893         $1.829         $1.649         $1.380         $1.220         $1.236             --
Number of Units
  Outstanding, End of
  Period                     19,261,448     22,910,908     22,132,206     21,338,267     21,538,113      8,548,091             --
 
GROWTH STOCK DIVISION
  Beginning of Period+           $1.991         $1.552         $1.300         $1.006         $1.000             --             --
  End of Period                  $2.491         $1.991         $1.552         $1.300         $1.006             --             --
 
Number of Units
  Outstanding, End of
  Period                      7,215,894      6,045,075      4,845,965      2,970,905      1,311,686             --             --
 
GROWTH AND INCOME STOCK
  DIVISION
  Beginning of Period+           $1.959         $1.525         $1.287         $0.994         $1.000             --             --
  End of Period                  $2.382         $1.959         $1.525         $1.287         $0.994             --             --
 
Number of Units
  Outstanding, End of
  Period                     10,866,893      8,963,724      7,054,484      5,605,215      3,129,287             --             --
 
INDEX 500 STOCK DIVISION
  Beginning of Period*           $3.175         $2.414         $1.991         $1.469         $1.470         $1.356         $1.280
  End of Period                  $4.037         $3.175         $2.414         $1.991         $1.469         $1.470         $1.356
 
Number of Units
  Outstanding, End of
  Period                     21,467,931     21,531,879     20,092,060     18,961,291     17,624,809     16,051,619      4,774,008
 
BALANCED DIVISION
  Beginning of Period            $5.768         $4.806         $4.290         $3.436         $3.480         $3.216         $3.092
  End of Period                  $6.771         $5.768         $4.806         $4.290         $3.436         $3.480         $3.216
 
Number of Units
  Outstanding, End of
  Period                     40,487,926     44,638,127     48,457,793     52,575,295     59,200,252     63,940,609     62,756,051
 
HIGH YIELD BOND DIVISION
  Beginning of Period+           $1.595         $1.394         $1.178         $1.022         $1.000             --             --
  End of Period                  $1.546         $1.595         $1.394         $1.178         $1.022             --             --
 
Number of Units
  Outstanding, End of
  Period                      3,974,656      3,770,055      2,456,295      1,609,770      1,215,989             --             --
 
SELECT BOND DIVISION
  Beginning of Period            $6.703         $6.201         $6.078         $5,167         $5.384         $4.941         $4.677
  End of Period                  $7.088         $6.703         $6.201         $6.078         $5.167         $5.384         $4.941
 
Number of Units
  Outstanding, End of
  Period                      2,171,879      2,252,704      2,691,481      2,778,441      2,923,557      2,917,137      2,667,880
 
MONEY MARKET DIVISION
  Beginning of Period            $2.335         $2.241         $2.156         $2.063         $2.007         $1.976         $1.936
  End of Period                  $2.431         $2.335         $2.241         $2.156         $2.063         $2.007         $1.976
 
Number of Units
  Outstanding, End of
  Period                      6,699,739      6,270,333      7,029,739      7,896,022      8,608,326      7,614,186      8,478,941
 
<CAPTION>
 
                               1991           1990           1989
                           ------------   ------------   ------------
<S>                        <C>            <C>            <C>
AGGRESSIVE GROWTH STOCK
  DIVISION
  Beginning of Period*           $1.010         $1.000             --
  End of Period                  $1.556         $1.010             --
  Number of Units
  Outstanding, End of
   Period                     3,208,965         81,406             --
INTERNATIONAL EQUITY
  DIVISION
  Beginning of Period**              --             --             --
  End of Period                      --             --             --
Number of Units
  Outstanding, End of
  Period                             --             --             --
GROWTH STOCK DIVISION
  Beginning of Period+               --             --             --
  End of Period                      --             --             --
Number of Units
  Outstanding, End of
  Period                             --             --             --
GROWTH AND INCOME STOCK
  DIVISION
  Beginning of Period+               --             --             --
  End of Period                      --             --             --
Number of Units
  Outstanding, End of
  Period                             --             --             --
INDEX 500 STOCK DIVISION
  Beginning of Period*           $1.000         $1.000             --
  End of Period                  $1.280         $1.000             --
Number of Units
  Outstanding, End of
  Period                      2,593,051         30,451             --
BALANCED DIVISION
  Beginning of Period            $2.526         $2.531         $2.217
  End of Period                  $3.092         $2.526         $2.531
Number of Units
  Outstanding, End of
  Period                     59,013,262     58,632,612     59,790,768
HIGH YIELD BOND DIVISION
  Beginning of Period+               --             --             --
  End of Period                      --             --             --
Number of Units
  Outstanding, End of
  Period                             --             --             --
SELECT BOND DIVISION
  Beginning of Period            $4.052         $3.787         $3.368
  End of Period                  $4.677         $4.052         $3.787
Number of Units
  Outstanding, End of
  Period                      2,087,901      1,970,476      2,102,874
MONEY MARKET DIVISION
  Beginning of Period            $1.855         $1.739         $1.615
  End of Period                  $1.936         $1.855         $1.739
Number of Units
  Outstanding, End of
  Period                      9,098,558     10,506,714      8,094,998
</TABLE>
 
 * The initial investments in the Aggressive Growth Stock Division and Index 500
   Stock Division were made on December 12, 1990.
 
 ** The initial investment in the International Equity Division was made on
    April 30, 1993.
 
 + The initial investments in the Growth Stock Division, Growth and Income Stock
   Division, and High Yield Bond Division were made on May 3, 1994.
 
                                       --
                                       7
<PAGE>
ACCUMULATION UNIT VALUES
 
CONTRACTS ISSUED PRIOR TO DECEMBER 17, 1981
<TABLE>
<CAPTION>
                                                           FOR THE YEARS ENDED DECEMBER 31
                           -----------------------------------------------------------------------------------------------
                              1998          1997          1996          1995          1994          1993          1992
                           -----------   -----------   -----------   -----------   -----------   -----------   -----------
<S>                        <C>           <C>           <C>           <C>           <C>           <C>           <C>
AGGRESSIVE GROWTH STOCK
  DIVISION
  Beginning of Period*          $3.714        $3.286        $2.813        $2.035        $1.945        $1.645        $1.564
  End of Period                 $3.965        $3.714        $3.286        $2.813        $2.035        $1.945        $1.645
 
Number of Units
  Outstanding, End of
  Period                       479,410       640,838       890,850       861,229       805,409       602,390       459,581
 
INTERNATIONAL EQUITY
  DIVISION
  Beginning of Period**         $1.872        $1.680        $1.398        $1.230        $1.240        $1.000            --
  End of Period                 $1.947        $1.872        $1.680        $1.398        $1.230        $1.240            --
 
Number of Units
  Outstanding, End of
  Period                       647,767     1,297,660     1,332,812     1,166,796     1,529,309       912,421            --
 
GROWTH STOCK DIVISION
  Beginning of Period+          $2.027        $1.573        $1.311        $1.009            --            --            --
  End of Period                 $2.549        $2.027        $1.573        $1.311            --            --            --
 
Number of Units
  Outstanding, End of
  Period                       247,491       327,731       118,168         1,782            --            --            --
 
GROWTH AND INCOME STOCK
  DIVISION
  Beginning of Period+          $1.995        $1.546        $1.298        $0.997            --            --            --
  End of Period                 $2.438        $1.995        $1.546        $1.298            --            --            --
 
Number of Units
  Outstanding, End of
  Period                       310,014       348,188        69,566         9,498            --            --            --
 
INDEX 500 STOCK DIVISION
  Beginning of Period*          $3.289        $2.488        $2.042        $1.499        $1.492        $1.370        $1.287
  End of Period                 $4.202        $3.289        $2.488        $2.042        $1.499        $1.492        $1.370
 
Number of Units
  Outstanding, End of
  Period                     7,343,357     8,175,537     9,600,286    10,111,615    10,735,943    12,320,684       242,871
 
BALANCED DIVISION
  Beginning of Period           $6.248        $5.180        $4.601        $3.667        $3.695        $3.398        $3.250
  End of Period                 $7.372        $6.248        $5.180        $4.601        $3.667        $3.695        $3.398
 
Number of Units
  Outstanding, End of
  Period                     3,013,626     3,845,538     4,743,812     5,651,599     6,525,821     7,060,303     8,324,438
 
HIGH YIELD BOND DIVISION
  Beginning of Period+          $1.624        $1.412        $1.188        $1.025            --            --            --
  End of Period                 $1.582        $1.624        $1.412        $1.188            --            --            --
 
Number of Units
  Outstanding, End of
  Period                       183,181       600,752       428,588            --            --            --            --
 
SELECT BOND DIVISION
  Beginning of Period           $7.263        $6.685        $6.520        $5.515        $5.719        $5.222        $4.918
  End of Period                 $7.719        $7.263        $6.685        $6.520        $5.515        $5.719        $5.222
 
Number of Units
  Outstanding, End of
  Period                       899,839     1,012,083     1,215,131     1,172,420     1,266,751     1,389,667     1,411,347
 
MONEY MARKET DIVISION
  Beginning of Period           $2.529        $2.416        $2.312        $2.201        $2.131        $2.088        $2.035
  End of Period                 $2.646        $2.529        $2.416        $2.312        $2.201        $2.131        $2.088
 
Number of Units
  Outstanding, End of
  Period                     1,723,332       893,452     1,103,625     1,264,988     1,020,911       788,050     1,231,018
 
<CAPTION>
 
                              1991          1990           1989
                           -----------   -----------   ------------
<S>                        <C>           <C>           <C>
AGGRESSIVE GROWTH STOCK
  DIVISION
  Beginning of Period*          $1.010        $1.000             --
  End of Period                 $1.564        $1.010             --
Number of Units
  Outstanding, End of
  Period                       262,149         9,478             --
INTERNATIONAL EQUITY
  DIVISION
  Beginning of Period**             --            --             --
  End of Period                     --            --             --
Number of Units
  Outstanding, End of
  Period                            --            --             --
GROWTH STOCK DIVISION
  Beginning of Period+              --            --             --
  End of Period                     --            --             --
Number of Units
  Outstanding, End of
  Period                            --            --             --
GROWTH AND INCOME STOCK
  DIVISION
  Beginning of Period+              --            --             --
  End of Period                     --            --             --
Number of Units
  Outstanding, End of
  Period                            --            --             --
INDEX 500 STOCK DIVISION
  Beginning of Period*          $1.000        $1.000             --
  End of Period                 $1.287        $1.000             --
Number of Units
  Outstanding, End of
  Period                        33,349        13,511             --
BALANCED DIVISION
  Beginning of Period           $2.642        $2.635         $2.296
  End of Period                 $3.250        $2.642         $2.635
Number of Units
  Outstanding, End of
  Period                     8,795,056     9,637,964     11,002,773
HIGH YIELD BOND DIVISION
  Beginning of Period+              --            --             --
  End of Period                     --            --             --
Number of Units
  Outstanding, End of
  Period                            --            --             --
SELECT BOND DIVISION
  Beginning of Period           $4.239        $3.943         $3.488
  End of Period                 $4.918        $4.239         $3.943
Number of Units
  Outstanding, End of
  Period                     1,590,698     1,590,884      1,854,807
MONEY MARKET DIVISION
  Beginning of Period           $1.940        $1.810         $1.673
  End of Period                 $2.035        $1.940         $1.810
Number of Units
  Outstanding, End of
  Period                     1,393,920     2,143,153      1,590,479
</TABLE>
 
 * The initial investments in the Index 500 Stock Division and Aggressive Growth
   Stock Division were made on December 12, 1990.
 
 ** The initial investment in the International Equity Division was made on
    April 30, 1993.
 
 + The initial investments in the Growth Stock Division, Growth and Income Stock
   Division, and High Yield Bond Division were made on May 3, 1994.
 
                                       --
                                       8
<PAGE>
THE COMPANY
 
The Northwestern Mutual Life Insurance Company was organized by a special act of
the Wisconsin Legislature in 1857. It is the nation's fourth largest life
insurance company, based on total assets in excess of $77 billion on December
31, 1998, and is licensed to conduct a conventional life insurance business in
the District of Columbia and in all states of the United States. Northwestern
Mutual Life sells life and disability income insurance policies and annuity
contracts through its own field force of approximately 6,000 full time producing
agents. The Home Office of Northwestern Mutual Life is located at 720 East
Wisconsin Avenue, Milwaukee, Wisconsin 53202.
 
"We" in this prospectus means Northwestern Mutual Life.
 
- --------------------------------------------------------------------------------
 
NML VARIABLE ANNUITY ACCOUNT A
 
We established the Account on February 14, 1968 by action of our Board of
Trustees in accordance with the provisions of the Wisconsin insurance law.
 
The Account has sixteen Divisions. The money you invest to provide variable
benefits under your Contract is placed in one or more of the Divisions as you
direct.
 
Under Wisconsin law, the investment operations of the Account are kept separate
from our other operations. The values for your Contract will not be affected by
income, gains or losses for the rest of our business. The income, gains or
losses, realized or unrealized, for the assets we place in the Account for your
Contract will determine the value of your Contract benefits and will not affect
the rest of our business. The assets in the Account are reserved for you and
other Contract owners, although the assets belong to us and we do not hold the
assets as a trustee. We and our creditors cannot reach those assets to satisfy
other obligations until our obligations under your Contract have been satisfied.
But all of our assets (except those we hold in some other separate accounts) are
available to satisfy our obligations under your Contract.
 
The Account is not registered as an investment company under the Investment
Company Act of 1940.
 
- --------------------------------------------------------------------------------
 
THE FUNDS
 
Northwestern Mutual Series Fund, Inc. is composed of eleven separate portfolios
which operate as separate mutual funds. The portfolios are the Small Cap Growth
Stock Portfolio, Aggressive Growth Stock Portfolio, International Equity
Portfolio, Index 400 Stock Portfolio, Growth Stock Portfolio, Growth and Income
Stock Portfolio, Index 500 Stock Portfolio, Balanced Portfolio, High Yield Bond
Portfolio, Select Bond Portfolio and Money Market Portfolio. The Account buys
shares of each Portfolio at net asset value, that is, without any sales charge.
 
Northwestern Mutual Investment Services, LLC ("NMIS"), our wholly-owned
subsidiary, is the investment adviser to the Fund. We provide the people and
facilities that NMIS uses in performing its investment advisory functions, and
we are a party to the investment advisory agreement. NMIS has retained J.P.
Morgan Investment Management, Inc. and Templeton Investment Counsel, Inc. under
investment sub-advisory agreements to provide investment advice to the Growth
and Income Stock Portfolio and the International Equity Portfolio.
 
The Russell Insurance Funds include five separate portfolios which operate as
separate mutual funds. These are the Multi-Style Equity Fund, Aggressive Equity
Fund, Non-U.S. Fund, Real Estate Securities Fund and Core Bond Fund. The Account
buys shares of each of the Russell Insurance Funds at net asset value, that is,
without any sales charge.
 
The assets of each of the Russell Insurance Funds are invested by one or more
investment management organizations researched and recommended by Frank Russell
Company ("Russell"), and an affiliate of Russell, Frank Russell Investment
Management Company ("FRIMCo"). FRIMCo also advises, operates and
 
                                       --
                                       9
<PAGE>
administers the Russell Insurance Funds. Russell is our majority-owned
subsidiary.
 
FOR MORE INFORMATION REGARDING THE MUTUAL FUNDS, INCLUDING INFORMATION ABOUT
THEIR INVESTMENT OBJECTIVES AND EXPENSES, SEE THE PROSPECTUSES FOR NORTH-
 
WESTERN MUTUAL SERIES FUND, INC. AND RUSSELL INSURANCE FUNDS ATTACHED TO THIS
PROSPECTUS. YOU SHOULD READ THE MUTUAL FUND PROSPECTUSES CAREFULLY BEFORE YOU
INVEST IN THE CONTRACTS.
 
- --------------------------------------------------------------------------------
 
THE CONTRACTS
 
PURCHASE PAYMENTS UNDER THE CONTRACTS
 
AMOUNT AND FREQUENCY  A purchase payment is the money you give us to pay for
your Contract. You may make purchase payments monthly, quarterly, semiannually,
annually or on any other frequency acceptable to us.
 
For Back Load Contracts the minimum amount for each purchase payment is $25. We
will accept larger purchase payments than due, or payments at other times, but
total purchase payments under any Contract may not exceed $5,000,000 without our
consent. For Front Load Contracts the minimum initial purchase payment is
$10,000. The minimum amount for each subsequent purchase payment is $25 for all
Contracts.
 
Purchase payments may not exceed the applicable federal income tax limits. See
"Federal Income Taxes", p. 15.
 
APPLICATION OF PURCHASE PAYMENTS  We credit net purchase payments, after
deduction of any sales load, to the Account and allocate them to one or more
Divisions as you direct. We then invest those assets in shares of the Portfolio
or Fund which corresponds to that Division.
 
We apply purchase payments to provide "Accumulation Units" in one or more
Divisions. Accumulation Units represent your interest in the Account. The number
of Accumulation Units you receive for each net purchase payment is determined by
dividing the amount of the purchase payment to be allocated to a Division by the
value of an Accumulation Unit in that Division, based upon the next valuation of
the assets of the Division we make after we receive your purchase payment at our
Home Office. Receipt of purchase payments at a lockbox facility we have
designated will be considered the same as receipt at the Home Office. We value
assets as of the close of trading on the New York Stock Exchange for each day
the Exchange is open, and at any other time required by the Investment Company
Act of 1940.
 
The number of your Accumulation Units will be increased by additional purchase
payments or transfers into the Account and decreased by withdrawals or transfers
out of the Account. The investment experience of the Account does not change the
number (as distinguished from the value) of your Accumulation Units.
 
The value of an Accumulation Unit in each Division varies with the investment
experience of the Division (which in turn is determined by the investment
experience of the corresponding Portfolio or Fund). We determine the value by
multiplying the value on the immediately preceding valuation date by the net
investment factor for the Division. (See "Net Investment Factor", below.) Since
you bear the investment risk, there is no guarantee as to the aggregate value of
your Accumulation Units. That value may be less than, equal to, or more than the
cumulative net purchase payments you have made.
 
You may direct all or part of a purchase payment to the Guaranteed Interest
Fund. Amounts you direct to the Guaranteed Interest Fund will be invested on a
fixed basis. See "The Guaranteed Interest Fund", p. 14.
 
NET INVESTMENT FACTOR
 
For each Division the net investment factor for any period ending on a valuation
date is 1.000000 plus the net investment rate for the Division for that period.
Under the Contract the net investment rate is related to the assets of the
Division. However, since all amounts are simultaneously invested in shares of
the corresponding Portfolio or Fund when allocated to the Division, calculation
of the net investment rate for each of the Divisions may also be based upon the
change in value of a single share of the corresponding Portfolio or Fund.
 
                                       --
                                       10
<PAGE>
Thus, for example, in the case of the Balanced Division the net investment rate
is equal to (a) the change in the net asset value of a Balanced Portfolio share
for the period from the immediately preceding valuation date up to and including
the current valuation date, plus the per share amount of any dividends and other
distributions made by the Balanced Portfolio during the valuation period, less a
deduction for any applicable taxes or for any expenses resulting from a
substitution of securities, (b) divided by the net asset value of a Balanced
Portfolio share on the valuation date immediately preceding the current
valuation date, (c) less an adjustment to provide for the deduction for
mortality rate and expense risks that we have assumed. (See "Deductions", p.
16.) A penalty tax will apply to premature payments of Contract benefits. A
penalty tax of 10% of the amount of the payment which is includible in income
will be imposed on non-exempt withdrawals under individual retirement annuities,
tax deferred annuities and nonqualified deferred annuities. Payments which are
exempt from the penalty tax include payments upon disability, after age 59 1/2
or as substantially equal periodic payments for life.
 
The Portfolios and Funds will distribute investment income and realized capital
gains to the Account Divisions. We will reinvest those distributions in
additional shares of the same Portfolio or Fund. Unrealized capital gains and
realized and unrealized capital losses will be reflected by changes in the value
of the shares held by the Account.
 
BENEFITS PROVIDED UNDER THE CONTRACTS
 
The benefits provided under the Contracts consist of a withdrawal amount, a
death benefit and a maturity benefit. Subject to the restrictions noted below,
we will pay all of these benefits in a lump sum or under the payment plans
described below.
 
WITHDRAWAL AMOUNT  On or prior to the maturity date you are entitled to withdraw
the Accumulation Units credited to your Contract and receive the value thereof
less the applicable withdrawal charge. (See "Withdrawal Charge", p. 17.) The
value, which may be either greater or less than the amount you paid, is
determined as of the valuation date coincident with or next following our
receipt of your written request for withdrawal on a form we provide. The forms
are available from our Home Office and our agents. You may withdraw a portion of
the Accumulation Units on the same basis, except that we will not grant a
partial withdrawal which would result in less than 100 Accumulation Units
remaining; we will treat a request for such a partial withdrawal as a request to
surrender the entire Contract. Amounts distributed to an Annuitant upon
withdrawal of all or a portion of Accumulation Units may be subject to federal
income tax. (See "Federal Income Taxes", p. 15.) A 10% penalty tax may be
imposed on the taxable portion of premature payments of benefits (prior to age
59 1/2 or disability) unless payments are made after the employee separates from
service and payments are either paid in substantially equal installments over
the life or life expectancy of the employee or are paid on account of early
retirement after age 55.
 
If annuity payments are being made under Payment Plan 1 the payee may surrender
the Contract and receive the value of the Annuity Units credited to his
Contract, less the applicable withdrawal charge. (See "Withdrawal Charge", p.
17.) Upon death during the certain period of the payee under Plan 2 or both
payees under Plan 3, the beneficiary may surrender the Contract and receive the
withdrawal value of the unpaid payments for the certain period. The withdrawal
value is based on the Annuity Unit value on the withdrawal date, with the unpaid
payments discounted at the Assumed Investment Rate. (See "Description of Payment
Plans", p. 12.)
 
DEATH BENEFIT  Upon the death of the Annuitant prior to the maturity date, we
will pay to the direct beneficiary a death benefit equal to the Contract value,
as of the valuation date coincident with or next following the date on which
proof of death is received at our Home Office or, if later, the date on which
the beneficiary elects a method of payment. If death occurs prior to the
Annuitant's 65th birthday the death benefit, where permitted by state law, will
be not less than the amount of purchase payments we received under the Contract,
less withdrawals. The death benefit may be paid either in a lump sum or under a
payment plan.
 
MATURITY BENEFIT  Purchase payments under the Contract are payable until the
maturity date specified in the Contract. You may select any date up to age 90 as
the maturity date, subject to applicable tax law requirements. On the maturity
date, if you have not elected any other permissible payment plan, we will change
the maturity date to the Contract anniversary nearest the Annuitant's 90th
birthday. On that date, if you have not elected any other permissible payment
plan, we will pay the value of the Contract in monthly
 
                                       --
                                       11
<PAGE>
payments for life under a variable payment plan with payments certain for ten
years.
 
VARIABLE PAYMENT PLANS
 
We will pay part or all of the benefits under a Contract under a variable
payment plan you select. The payment plan starts on the maturity date. See
"Maturity Benefit", above. Under a variable plan, you bear the entire investment
risk, since we make no guarantees of investment return. Accordingly, there is no
guarantee of the amount of the variable payments, and you must expect the amount
of such payments to change from month to month. For a discussion of tax
considerations and limitations regarding the election of payment plans, see
"Federal Income Taxes", p. 15.
 
DESCRIPTION OF PAYMENT PLANS  The following payment plans are available:
 
1.  PAYMENTS FOR A CERTAIN PERIOD.  An annuity payable monthly for a specified
period of five to 30 years.
 
2.  LIFE ANNUITY WITH OR WITHOUT CERTAIN PERIOD.  An annuity payable monthly
until the payee's death, or until the expiration of a selected certain period,
whichever is later. After the payee's death during the certain period, if any,
we will make payments as they are due to the designated contingent beneficiary.
You may select a certain period of either 10 or 20 years, or you may choose a
plan with no certain period.
 
3.  JOINT AND SURVIVOR LIFE ANNUITY WITH CERTAIN PERIOD. An annuity payable
monthly for a certain period of 10 years and thereafter to two persons for their
joint lives. On the death of either payee, payments continue for the remainder
of the 10 years certain or the remaining lifetime of the survivor, whichever is
longer.
 
We may limit the election of a payment plan to one that results in an initial
payment of at least $20. A payment plan will continue even if payments fall to
less than $20 after the payment plan begins.
 
From time to time we may establish payment plan rates with greater actuarial
value than those stated in the Contract and make them available at the time of
settlement. We may also make available other payment plans, with provisions and
rates we publish for those plans.
 
AMOUNT OF ANNUITY PAYMENTS  We will determine the amount of the first annuity
payment on the basis of the particular payment plan you select, the annuity
payment rate and, for plans involving life contingencies, the Annuitant's
adjusted age. We will calculate the amount of the first annuity payment on a
basis that takes into account the length of time over which we expect annuity
payments to continue. The first payment will be lower for an Annuitant who is
younger when payments begin, and higher for an Annuitant who is older, if the
payment plan involves life contingencies. The first payment will be lower if the
payment plan includes a longer certain period. Variable annuity payments after
the first will vary from month to month to reflect the fluctuating value of the
Annuity Units credited to your Contract. Annuity Units represent the interest of
the Contract in each Division of the Account after annuity payments begin.
 
ASSUMED INVESTMENT RATE  The variable annuity rate tables for the Contracts are
based upon an Assumed Investment Rate of 3 1/2%. Variable annuity rate tables
based upon an Assumed Investment Rate of 5% are also available where permitted
by state law.
 
The Assumed Investment Rate affects both the amount of the first variable
payment and the amount by which subsequent payments increase or decrease. The
Assumed Investment Rate does not affect the actuarial value of the future
payments as of the date when payments begin, though it does affect the actual
amount which may be received by an individual Annuitant.
 
Over a period of time, if each Division achieved a net investment result exactly
equal to the Assumed Investment Rate applicable to a particular payment plan,
the amount of annuity payments would be level. However, if the Division achieved
a net investment result greater than the Assumed Investment Rate, the amount of
annuity payments would increase. Similarly, if the Division achieved a net
investment result smaller than the Assumed Investment Rate, the amount of
annuity payments would decrease.
 
A higher Assumed Investment Rate will result in a larger initial payment but
more slowly rising and more rapidly falling subsequent payments than a lower
Assumed Investment Rate.
 
ADDITIONAL INFORMATION
 
TRANSFERS BETWEEN DIVISIONS AND PAYMENT PLANS You may change the allocation of
purchase payments among the Divisions and transfer values from one
 
                                       --
                                       12
<PAGE>
Division to another both before and after annuity payments begin. In order to
take full advantage of these features you should carefully consider, on a
continuing basis, which Division or apportionment is best suited to your
long-term investment needs.
 
You may at any time change the allocation of purchase payments among the
Divisions by written notice to us. Purchase payments we receive at our Home
Office on and after the date on which we receive the notice will be applied to
provide Accumulation Units in one or more Divisions on the basis of the new
allocation.
 
Before the effective date of a payment plan you may, upon written request,
transfer Accumulation Units from one Division to another. After the effective
date of a payment plan the payee may transfer Annuity Units from one Division to
another. We will adjust the number of Accumulation or Annuity Units to be
credited to reflect the respective value of the Accumulation and Annuity Units
in each of the Divisions. For Accumulation Units the minimum amount which may be
transferred is the lesser of $100 or the entire value of the Accumulation Units
in the Division from which the transfer is being made. For each transfer
beginning with the thirteenth in any Contract year we may deduct a transfer fee
of $25 from the amount transferred. We currently make no charge for transfers.
 
If you contemplate the transfer of funds from one Division to another, you
should consider the risk inherent in a switch from one investment medium to
another. In general, frequent transfers based on short-term expectations for the
stock and bond markets, especially transfers of large sums, will tend to
accentuate the danger that a transfer will be made at an inopportune time.
 
You may transfer amounts which you have invested on a fixed basis to any
Division of the Account, and the value of Accumulation Units in any Division of
the Account to the Guaranteed Interest Fund for investment on a fixed basis,
subject to the restrictions described in the Contract. See "The Guaranteed
Interest Fund", p. 14.
 
After the effective date of a payment plan which does not involve a life
contingency (i.e., Plan 1) a payee may transfer to either form of life annuity
at no charge. We will apply the value of the remaining payments to the new plan
selected. We will determine the amount of the first annuity payment under the
new plan on the basis of the particular plan selected, the annuity payment rate
and the Annuitant's adjusted age and sex. Subsequent payments will vary to
reflect changes in the value of the Annuity Units credited. We permit other
transfers between payment plans subject to such limitations we may reasonably
determine. Generally, however, we do not permit transfer from a payment plan
involving a life contingency to a payment plan which does not involve the same
life contingency.
 
You may make transfers from the Money Market Division at any time while a
payment plan is in force. The Contracts provide that transfers between the other
Divisions and transfers between payment plans may be made after the payment plan
has been in force for at least 90 days and thereafter whenever at least 90 days
have elapsed since the date of the last transfer. At present we permit transfers
at any time. We will make the transfer as of the close of business on the
valuation date coincident with or next following the date on which we receive
the request for transfer at our Home Office, or at a later date you request.
 
GENDER-BASED ANNUITY PAYMENT RATES  Federal law, and the laws of certain states,
may require that annuity considerations and annuity payment rates be determined
without regard to the sex of the Annuitant. Because we offer the Contracts for
use with HR-10 Plans where these rules may have general application, the annuity
payment rates in the Contracts do not distinguish between male and female
Annuitants. However, Contracts with sex-distinct rates are available on request.
Prospective purchasers of the Contracts should review any questions in this area
with qualified counsel.
 
OWNERS OF THE CONTRACTS  The Owner of the Contract has the sole right to
exercise all rights and privileges under the Contract, except as the Contract
otherwise provides. The Owner is ordinarily the retirement plan, but may be the
employer or the Annuitant or other person. The Annuitant is the person upon
whose life the Contract is issued and Contract benefits depend. Following the
death of the Annuitant any remaining Contract benefits are payable to a
beneficiary or contingent beneficiary named in the Contract. In this prospectus,
"you" means the Owner or a prospective purchaser of the Contract.
 
DEFERMENT OF BENEFIT PAYMENTS  We reserve the right to defer determination of
the withdrawal value of the Contracts, or the payment of benefits under a
variable payment plan, until after the end of any period during which the right
to redeem shares of either of the
 
                                       --
                                       13
<PAGE>
mutual funds is suspended, or payment of the redemption value is postponed, and
for any period during which the New York Stock Exchange is closed or trading
thereon is restricted or an emergency exists, so that valuation of the assets of
the Fund or disposal of securities they hold is not reasonably practical; or as
such deferment is otherwise permitted by applicable law.
 
DIVIDENDS  The Contracts share in our divisible surplus, except while payments
are being made under a variable payment plan. Our divisible surplus is
determined annually for the following year. State law requires that we
distribute the surplus equitably among participating contracts. Distributions of
divisible surplus are commonly referred to as "dividends".
 
We are paying dividends on approximately 18% of our inforce variable annuity
contracts in 1999. Dividends are not guaranteed to be paid in future years. The
dividend amount is volatile since it is based on the average variable Contract
value which is defined as the value of the Accumulation units on the last
Contract anniversary adjusted to reflect any transactions since that date which
increased or decreased the Contract's interest in the Account.
 
Dividends on variable annuities arise principally as a result of more favorable
expense experience than that which we assumed in determining deductions. Such
favorable experience is generated primarily by older and/or larger Contracts,
which have a mortality rate and expense risk charge of at least 0.75%. In
general, we are not paying dividends on Contracts with an average variable
Contract value of less than $30,000, and about 75% of those with a value above
$30,000 will receive dividends. The expected dividend payout for 1999 represents
about 0.39% of the average variable Contract value for those Contracts that will
receive dividends. The maximum dividend we are paying on a specific contract is
about 0.70%.
 
We pay any dividend for a Contract on the anniversary date of that Contract. We
apply the dividend as a net purchase payment unless you elect to have the
dividend paid in cash.
 
SUBSTITUTION AND CHANGE  Pursuant to authority of our Board of Trustees, (a) we
may invest the assets of a Division in securities of another mutual fund or
another issuer, instead of the Portfolio or Fund in which you have invested, as
a substitute for the shares you already have or as the securities to be
purchased in the future, or (b) we may modify the provisions of the Contracts to
assure qualification for the benefits provided by the provisions of the Internal
Revenue Code relating to retirement annuity or variable annuity contracts, or to
comply with any other applicable federal or state laws. In the event of any such
substitution or change, we may make appropriate endorsement on Contracts having
an interest in the Account and take such other action as may be necessary to
effect the substitution or change.
 
FIXED ANNUITY PAYMENT PLANS  We will also pay Contract benefits under fixed
annuity payment plans which are not described in this Prospectus. If you select
a fixed annuity, we will cancel the Accumulation Units credited to your Deferred
Contract, we will transfer the withdrawal value of the Contract to our general
account, and you will no longer have any interest in the Account. We may make a
withdrawal charge in determining the withdrawal value. (See "Withdrawal Amount",
p. 11, and "Withdrawal Charge", p. 17.)
 
FINANCIAL STATEMENTS  Financial statements of the Account and financial
statements of Northwestern Mutual Life appear in the Statement of Additional
Information.
 
- --------------------------------------------------------------------------------
 
THE GUARANTEED INTEREST FUND
 
You may direct all or part of your purchase payments to the Guaranteed Interest
Fund for investment on a fixed basis. You may transfer amounts previously
invested in the Account Divisions to the Guaranteed Interest Fund, prior to the
maturity date, and you may transfer amounts in the Guaranteed Interest Fund to
the Account Divisions. In each case these transfers are subject, to the
restrictions described in the Contract.
 
Amounts you invest in the Guaranteed Interest Fund become part of our general
assets. In reliance on certain exemptive and exclusionary provisions, we have
not registered interests in the Guaranteed Interest Fund under the Securities
Act of 1933 and we have not registered the Guaranteed Interest Fund as an
investment company under the Investment Company Act of 1940. Accordingly,
neither the Guaranteed Interest Fund nor any interests therein are generally
subject to these Acts. We have been advised that the staff of the Securities and
Exchange Commission has not reviewed the disclosure in this prospectus relating
to the Guaranteed Interest Fund. This disclosure, however, may be subject to
certain generally applicable provisions of the federal securities laws relating
to the accuracy and completeness of statements made in prospectuses.
 
                                       --
                                       14
<PAGE>
Amounts you invest in the Guaranteed Interest Fund earn interest at rates we
declare from time to time. We will guarantee the interest rate for each amount
for at least one year. The interest rate will be at an annual effective rate of
at least 3%. At the expiration of the period for which we guarantee the interest
rate, a new interest rate may apply. We credit interest and compound it daily.
We determine the effective date for a transaction involving the Guaranteed
Interest Fund in the same manner as the effective date for a transaction
involving a Division of the Account.
 
Investments in the Guaranteed Interest Fund are subject to a maximum limit of
$1,000,000 ($250,000 in New York) without our prior consent. To the extent that
a purchase payment or transfer from a Division of the Account causes the
Contract's interest in the Guaranteed Interest Fund to exceed this maximum
limit, we will place the amount of the excess in the Money Market Division and
it will remain there until the you instruct us otherwise.
 
Transfers from the Guaranteed Interest Fund to the Account Divisions are subject
to limits. After a transfer from the Guaranteed Interest Fund we will allow no
further transfers from the Guaranteed Interest Fund for a period of 365 days; in
addition, we will allow no further transfers back into the Guaranteed Interest
Fund for a period of 90 days. The maximum amount that you may transfer from the
Guaranteed Interest Fund in one transfer is the greater of (1) 25% of the amount
that you had invested in the Guaranteed Interest Fund as of the last Contract
anniversary preceding the transfer and (2) the amount of your most recent
transfer from the Guaranteed Interest Fund. But in no event will this maximum
transfer amount be less than $1,000 or more than $50,000. (The $50,000 limit
does not apply in New York.)
 
The deduction for mortality rate and expense risks, as described below, is not
assessed against amounts in the Guaranteed Interest Fund, and amounts in the
Guaranteed Interest Fund do not bear any expenses of either of the mutual funds.
Other charges under the Contracts apply for amounts in the Guaranteed Interest
Fund as they are described in this prospectus for amounts you invest on a
variable basis. See "Deductions", p. 16. For purposes of allocating and
deducting the annual Contract fee, we consider any investment in the Guaranteed
Interest Fund as though it were an investment of the same amount in one of the
Account Divisions.
 
- --------------------------------------------------------------------------------
 
FEDERAL INCOME TAXES
 
We offer the Contracts only for use under tax-qualified plans meeting the
requirements of Sections 401 and 403(a) of the Code. However, in the event
Contracts should be issued pursuant to HR-10 Plans, trusts or custodial accounts
which at the time of issuance are not qualified under the Code, some or all of
the tax benefits described herein may be lost.
 
CONTRIBUTION LIMITS
 
Any employer, including a self-employed person, can establish a plan under
Section 401(a) or 403(a) for participating employees. As a general rule, annual
contributions to a defined contribution plan made by the employer and the
employee cannot exceed the lesser of $30,000 or 25% of compensation or earned
income (up to $160,000, indexed).
 
Qualified plans are subject to minimum coverage, nondiscrimination and spousal
consent requirements. In addition, "top heavy" rules apply if more than 60% of
the contributions or benefits are allocated to certain highly compensated
employees. Violations of the contribution limits or other requirements may
disqualify the plan and/or subject the employer to taxes and penalties.
 
TAXATION OF CONTRACT BENEFITS
 
No tax is payable as a result of any increase in the value of a Contract until
benefits from the Contract are received. Benefits received as annuity payments
will be taxable as ordinary income when received in accordance with Section 72
of the Code. As a general rule, where an employee makes nondeductible
contributions to the Plan, the payee may exclude from income that portion of
each benefit payment which represents a return of the employee's "investment in
the contract" as defined in Section 72 until the entire "investment in the
contract" is recovered. A 50% penalty tax may be imposed on payments to the
extent they are less than certain required minimum amounts. In addition, a 10%
penalty tax may be imposed on benefits paid in excess of the benefits provided
under the Plan formula if the payee is or was a "5% owner" of the employer while
a participant in the Plan.
 
                                       --
                                       15
<PAGE>
Benefits paid in a form other than an annuity will be taxed as ordinary income
when received except for that portion of the payment, if any, which represents a
return of the employee's "investment in the contract." Benefits received as a
"lump sum distribution" may be eligible for a separate tax averaging calculation
and, with certain limited exceptions, all benefits are subject to the tax-free
rollover provisions of the Code. A 10% penalty tax may be imposed on the taxable
portion of premature payments of benefits (prior to age 59 1/2 or disability)
unless payments are made after the employee separates from service and payments
are either paid in substantially equal installments over the life or life
expectancy of the employee or are paid on account of early retirement after age
55 or unless payments are made for medical expenses in excess of 7.5% of the
employee's Adjusted Gross Income. A loan from the Plan to an employee, other
than an owner-employee, may be taxable as ordinary income depending on the
amount and terms of the loan. A loan to an owner-employee is a prohibited
transaction under the Code and could disqualify the Plan.
 
Benefit payments will be subject to mandatory 20% withholding unless (1) they
are rolled over directly to another tax-qualified plan or an individual
retirement arrangement, (2) they are paid in substantially equal installments
over the life or life expectancy of the employee (or of the employee and the
employee's beneficiary) or over a period of 10 years or more, or (3) they are
"required minimum distributions."
 
The rules governing Plan provisions, payments and deductions and taxation of
distributions from such Plans and Trusts, as set forth in the Code and the
regulations relating thereto, are complex and cannot be readily summarized.
Furthermore, special rules are applicable in many situations, and prospective
purchasers desiring to adopt an HR-10 pension or profit-sharing plan or trust
should consult qualified tax counsel.
 
TAXATION OF NORTHWESTERN MUTUAL LIFE
 
We may charge the appropriate Contracts with their shares of any tax liability
which may result from the maintenance or operation of the Divisions of the
Account. We are currently making no charge. (See "Net Investment Factor", p. 10
and "Deductions", below.)
 
- --------------------------------------------------------------------------------
 
DEDUCTIONS
 
We will make the following deductions:
 
1.  SALES LOAD.  For the Front Load Contract we deduct a sales load from all
purchase payments we receive. The sales load compensates us for the costs we
incur in selling the Contracts. We base the deduction on cumulative purchase
payments we have received and the rates in the table below:
 
<TABLE>
<CAPTION>
CUMULATIVE PURCHASE PAYMENTS
PAID UNDER THE CONTRACT                                   RATE
- -----------------------------------------------------  -----------
<S>                                                    <C>
First $100,000.......................................        4.0%
Next $400,000........................................        2.0%
Next $500,000........................................        1.0%
Balance over $1,000,000..............................        0.5%
</TABLE>
 
2.  DEDUCTIONS FOR MORTALITY RATE AND EXPENSE RISKS. The net investment factor
(see "Net Investment Factor", p. 10) we use in determining the value of
Accumulation and Annuity Units reflects a deduction on each valuation date for
mortality rate and expense risks we have assumed. For the Front Load Contract,
the deduction from Accumulation Units is at a current annual rate of 0.4% of the
assets of the Account, while the deduction from Annuity Units is zero. For the
Back Load Contract the deduction is at a current annual rate of 1.25% of the
assets of the Account. Our Board of Trustees may increase or decrease the
deduction, but in no event may the deduction exceed an annual rate of .75% for
the Front Load Contract and 1.50% for the Back Load Contract. This deduction is
the only expense item paid by the Account to date. The mutual funds pay expenses
which are described in the attached prospectuses for the mutual funds.
 
The risks we assume are (a) the risk that annuity payments will continue for
longer periods than anticipated because the Annuitants as a group live longer
than expected, and (b) the risk that the charges we make may be insufficient to
cover the actual costs we incur in connection with the Contracts. We assume
these risks for the duration of the Contract.
 
The net investment factor also reflects the deduction of any reasonable expenses
which may result if there were a substitution of other securities for shares of
the mutual funds as described under "Substitution and Change", p. 14, and any
applicable taxes, i.e., any tax
 
                                       --
                                       16
<PAGE>
liability we have paid or reserved for resulting from the maintenance or
operation of a Division of the Account, other than applicable premium taxes
which we may deduct directly from considerations. We do not presently anticipate
that we will make any deduction for federal income taxes (see "Federal Income
Taxes", p. 15), nor do we anticipate that maintenance or operation of the
Account will give rise to any deduction for state or local taxes. However, we
reserve the right to charge the appropriate Contracts with their shares of any
tax liability which may result under present or future tax laws from the
maintenance or operation of the Account or to deduct any such tax liability in
the computation of the net investment factor for such Contracts.
 
3.  CONTRACT FEE.  On each Contract anniversary prior to the maturity date we
make a deduction of $30 for administrative expenses relating to a Deferred
Contract during the prior year. We make the charge by reducing the number of
Accumulation Units credited to the Contract. For purposes of allocating and
deducting the annual Contract fee, we consider any investment in the Guaranteed
Interest Fund as though it were an investment of the same amount in one of the
Account Divisions. We cannot increase this charge. The charge is intended only
to reimburse us for our actual administrative expenses. We currently are waiving
the charge, if the Contract value on the Contract anniversary is $50,000 or
more.
 
4.  WITHDRAWAL CHARGE.  For the Back Load Contract if you withdraw Accumulation
Units for cash, we will deduct a withdrawal charge for sales expenses. This
charge compensates us for the expenses we incur in selling the Contracts. We
will base the withdrawal charge on the Amount Categories and the Rates in the
table below. We base the amount in each Category on cumulative purchase payments
you have made and on the number of Contract anniversaries that have occurred
since you made each purchase payment.
 
<TABLE>
<CAPTION>
AMOUNT CATEGORY                                             RATE
- ------------------------------------------------------     -----
<S>                                                     <C>
Eight.................................................           8%
Seven.................................................           7%
Six...................................................           6%
Five..................................................           5%
Four..................................................           4%
Three.................................................           3%
Two...................................................           2%
One...................................................           1%
Zero..................................................           0%
</TABLE>
 
The first $100,000 of total purchase payments paid over the life of the Contract
start out in Category Eight, the next $400,000 start out in Category Four, the
next $500,000 start out in Category Two, and all additional purchase payments
paid start out in Category One. As of each Contract anniversary, we move any
amount in a Category to the next lower Category until the Contract anniversary
on which that amount reaches Category Zero. The total withdrawal charge will be
the sum of all the results calculated by multiplying the amount in each Category
by the Rate for that Category. The amounts we use to calculate the withdrawal
charge will be limited to the value of the Contract benefits that are subject to
the withdrawal charge. The amounts we use will be taken from those Categories
that produce the lowest withdrawal charge. However, any amounts we use to
determine the charge for a partial withdrawal will not be used to determine
subsequent withdrawal charges. There is no withdrawal charge on the value of
Accumulation Units withdrawn in excess of the total purchase payments you have
paid under the Contract; but in the case of a partial withdrawal, we consider
the purchase payments paid under the Contract to be withdrawn first, except for
amounts eligible for the withdrawal charge free amount described in the next
paragraph.
 
The withdrawal charge free amount is available on a Contract if the Contract
value is at least $10,000 on the Contract anniversary preceding a withdrawal.
For each Contract year, the withdrawal charge free amount is equal to the lesser
of 10% of the Contract value on the last Contract anniversary, and the amount by
which the Contract value exceeds cumulative purchase payments as of the date of
the withdrawal. We will take eligible amounts withdrawn meeting these
requirements first from the portion of the Contract value that exceeds
cumulative purchase payments. We will base the withdrawal charge for any amounts
not included in the withdrawal charge free amount first on the purchase payments
that have been paid.
 
We will make no withdrawal charge when you select a variable payment plan.
However, we will make the withdrawal charge if you make a withdrawal, or partial
withdrawal, within five years after the beginning of a variable payment plan
which is not contingent on the payee's life (Plan 1). For fixed payment plans
the Contract provides for deduction of the withdrawal charge when the payment
plan is selected. By current administrative practice we will waive the
withdrawal charge upon selection of a fixed payment plan for a certain period of
12 years or more
 
                                       --
                                       17
<PAGE>
(Plan 1) or any fixed payment plan which involves a life contingency (Plans 2 or
3) if you select the payment plan after the Contract has been in force for at
least one full year.
 
5.  PREMIUM TAXES.  The Contracts provide for the deduction of applicable
premium taxes, if any, from purchase payments or from Contract benefits. Various
jurisdictions levy premium taxes. Premium taxes presently range from 0% to 2% of
total purchase payments. Many jurisdictions presently exempt from premium taxes
annuities such as the Contracts. As a matter of current practice, we do not
deduct premium taxes from purchase payments received under the Contracts or from
Contract benefits. However, we reserve the right to deduct premium taxes in the
future.
 
6.  EXPENSES FOR THE PORTFOLIOS AND FUNDS.  The expenses borne by the Portfolios
and Funds in which the assets of the Account are invested are described in the
prospectuses for Northwestern Mutual Series Fund, Inc. and the Russell Insurance
Funds. See the prospectuses attached to this prospectus.
 
CONTRACTS ISSUED PRIOR TO MARCH 31, 1995
 
For Contracts issued prior to March 31, 1995 and after December 16, 1981 there
is no front-end sales load but there is a surrender charge of 8% on the first
$25,000 of purchase payments, 4% on the next $75,000 and 2% on purchase payments
in excess of $100,000, based on total cumulative purchase payments paid under
the Contract. The surrender charge applicable for each purchase payment reduces
by 1% on each Contract anniversary. A withdrawal charge free amount is available
on the same basis described above for the current Contracts. See "Withdrawal
Charge", p. 17. The charge for mortality and expense risks for those Contracts
is 1.25% of the assets of the Account. The annual Contract fee is the lesser of
$30 or 1% of the Contract value. See the table of accumulation unit values on
page 7.
 
CONTRACTS ISSUED PRIOR TO DECEMBER 17, 1981
 
For Contracts issued prior to December 17, 1981 there is no surrender charge,
but purchase payments are subject to a deduction for sales expenses. The
deduction is 8% on the first $5,000 received during a single Contract year as
defined in the Contract, 4% on the next $20,000, 2% on the next $75,000 and 1%
on the excess over $100,000. The charge for mortality rate and expense risks for
those Contracts is .75% of the assets of the Account, which we may raise to a
maximum annual rate of 1%. There is no annual Contract fee. See the table of
accumulation unit values on page 8.
 
REDUCED CHARGES FOR EXCHANGE TRANSACTIONS
 
As a matter of current practice, we permit owners of fixed dollar annuities we
have previously issued to exchange those contracts for Front Load or Back Load
Contracts without paying a second charge for sales expenses. This rule is
subject to a number of exceptions and qualifications. We may change or withdraw
it at any time.
 
In general, we make a $25 administrative charge on these exchange transactions
and we permit only one such transaction in any 12-month period. Transactions on
this basis are subject to a limit of 20% of the amount held under the fixed
annuity contract in any 12-month period, but we are presently waiving this
limit.
 
Amounts exchanged from a fixed contract which provides for a surrender charge
are not charged for sales expenses when the exchange is effected. We place these
amounts in the same withdrawal charge category under the new Back Load Contract
as they were before.
 
We place exchange proceeds from fixed contracts which have no surrender charge
provisions in the 0% withdrawal charge category. As an alternative, exchange
proceeds from such a fixed contract may be added to a Front Load Contract or to
a Deferred Contract issued prior to December 17, 1981 without any deduction for
sales expenses.
 
Fixed annuity contracts (which are not described in this prospectus) are
available in exchange for the Contracts on a comparable basis.
 
                                       --
                                       18
<PAGE>
DISTRIBUTION OF THE CONTRACTS
 
We sell the Contracts through individuals who, in addition to being licensed
insurance agents of Northwestern Mutual Life, are registered representatives of
Northwestern Mutual Investment Services, LLC, our wholly-owned subsidiary.
Northwestern Mutual Investment Services, LLC is a registered broker-dealer under
the Securities Exchange Act of 1934, and a member of the National Association of
Securities Dealers. Where state law requires, these agents will also be licensed
securities salesmen. Commissions paid to the agents on sales of the Contracts
will not exceed 4% of purchase payments.
 
- --------------------------------------------------------------------------------
 
YEAR 2000 ISSUES
 
Since early 1996, we have been preparing for the computer requirements
associated with the approaching turn of the century. We completed assessment of
our internal systems in 1996. As of the date of this prospectus, the necessary
system changes are substantially complete. System testing is in process and we
expect testing of all critical systems to be completed during the first six
months of 1999.
 
The work on these computer systems extends to software packages we purchase from
vendors. In addition, we have been communicating formally with our business
partners to identify and assess potential exposure that could result from their
failure to address these computer issues on a timely basis. Each of our
departments has prepared a contingency plan.
 
We and our business partners bear all of the costs of identifying and resolving
the computer systems issues associated with the year 2000. These costs will have
no effect on the performance of the Account. The Contracts permit us to increase
the charges for our expense risks up to the guaranteed maximum rates. However,
we do not expect our costs for year 2000 compliance to have any significant
effect on the benefits or values provided by the Contracts.
 
We believe that our computer systems will be ready for the year 2000 well in
advance of the deadline. By their nature, however, the issues in this area carry
the risk of unforeseen problems, both at Northwestern Mutual Life and at all the
other sites where supporting functions and interaction take place. There can be
no assurance that these problems will not have a material adverse impact on the
operations of Northwestern Mutual Life and the Account.
 
                                       --
                                       19
<PAGE>
           TABLE OF CONTENTS FOR STATEMENT OF ADDITIONAL INFORMATION
<TABLE>
<CAPTION>
                                    Page
                                    ----
<S>                                 <C>
DISTRIBUTION OF THE CONTRACTS.....   B-2
DETERMINATION OF ANNUITY
  PAYMENTS........................   B-2
  Amount of Annuity Payments......   B-2
  Annuity Unit Value..............   B-3
  Illustrations of Variable
   Annuity Payments...............   B-3
VALUATION OF ASSETS OF THE
  ACCOUNT.........................   B-4
TRANSFERABILITY RESTRICTIONS......   B-4
EXPERTS...........................   B-4
 
<CAPTION>
                                    Page
                                    ----
<S>                                 <C>
FINANCIAL STATEMENTS OF THE
  ACCOUNT (for the two years ended
  December 31, 1998)..............   B-5
REPORT OF INDEPENDENT ACCOUNTANTS
  (for the two years ended
  December 31, 1998)..............  B-11
FINANCIAL STATEMENTS OF
  NORTHWESTERN MUTUAL LIFE (for
  the three years ended December
  31, 1998).......................  B-12
REPORT OF INDEPENDENT ACCOUNTANTS
  (for the three years ended
  December 31, 1998)..............  B-25
</TABLE>
 
- --------------------------------------------------------------------------------
 
This Prospectus sets forth concisely the information about NML Variable Annuity
Account A that a prospective investor ought to know before investing. Additional
information about Account A has been filed with the Securities and Exchange
Commission in a Statement of Additional Information which is incorporated herein
by reference. The Statement of Additional Information is available upon request
and without charge from The Northwestern Mutual Life Insurance Company. To
receive a copy, return the request form to the address listed below, or
telephone (414) 271-1444.
 
- --------------------------------------------------------------------------------
 
    TO:  The Northwestern Mutual Life Insurance Company
       Annuity and Accumulation Products Marketing Department
        Room E12J
       720 East Wisconsin Avenue
       Milwaukee, WI 53202
 
     Please send a Statement of Additional Information for NML Variable
     Annuity Account A to:
 
     Name __________________________________________________________________
 
     Address _______________________________________________________________
 
      ______________________________________________________________________
 
     City ______________________________ State ____________ Zip ____________
<PAGE>

More information about Northwestern Mutual Series Fund, Inc. is included in 
the Fund's Statement of Additional Information (SAI), incorporated by 
reference in this prospectus, which is available free of charge.

More information about the Fund's investments is included in the Fund's 
annual and semi-annual reports, which discuss the market conditions and 
investment strategies that significantly affected each Portfolio's 
performance during the previous fiscal period.

To request a free copy of the Fund's SAI, or current annual or semi-annual 
report, call us at 1-800-519-4665.  Information about the Fund (including the 
SAI) can be reviewed and copied at the Public Reference Room of the 
Securities and Exchange Commission (SEC) in Washington, DC.  Information on 
the operation of the Public Reference Room may be obtained by calling the SEC 
at 1-800-SEC-0330.  Reports and other information about the Fund are 
available on the SEC's Internet site at http://www.sec.gov.  Copies of the 
information may be obtained, upon payment of a duplicating fee by writing the 
Public Reference Section of the SEC, Washington, DC 20549-6009.

NORTHWESTERN MUTUAL LIFE


Individual Variable Annuity Contracts
for Retirement Plans of Self-Employed Persons
and Their Employees

NML Variable Annuity Account A
Northwestern Mutual Series Fund, Inc.
Russell Insurance Funds


90-1765 (4-99)

PROSPECTUSES

Investment Company Act File Nos. 811-3990 and 811-5371


NORTHWESTERN 
MUTUAL LIFE-Registered Trademark-
PO Box 3095
Milwaukee WI 53201-3095


Change Service Requested
<PAGE>

                        STATEMENT OF ADDITIONAL INFORMATION

                             VARIABLE ANNUITY CONTRACTS
        (for Retirement Plans of Self-Employed Perons and their Employees)

                           NML VARIABLE ANNUITY ACCOUNT A
                                  (the "Account"),
                          a separate investment account of
                   The Northwestern Mutual Life Insurance Company
                            ("Northwestern Mutual Life")

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

             This Statement of Additional Information is not a
             prospectus but supplements and should be read in
             conjunction with the prospectus for the Contracts.  A copy
             of the prospectus may be obtained from The Northwestern
             Mutual Life Insurance Company, 720 East Wisconsin Avenue,
             Milwaukee, Wisconsin 53202, telephone number (414) 271-1444.

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

          The Date of the Prospectus to which this Statement of
          Additional Information Relates is April 30, 1999.

          The Date of this Statement of Additional Information is April 30, 
          1999.


                                       B-1

<PAGE>

                           DISTRIBUTION OF THE CONTRACTS

     The Contracts are offered on a continuous basis exclusively through
individuals who, in addition to being life insurance agents of Northwestern
Mutual Life, are registered representatives of Northwestern Mutual Investment
Services, LLC ("NMIS").

     NMIS may be considered the underwriter of the Contracts for purposes of the
federal securities laws.  The following amounts of commissions were paid on
sales of the Contracts, including commissions on sales of variable annuity
contracts to corporate pension plans, during each of the last three years:

<TABLE>
<CAPTION>
                    Year          Amount
                    ----          ------
                    <S>         <C>
                    1998        $2,760,049
                    1997        $2,203,105
                    1996        $1,344,104
</TABLE>


                         DETERMINATION OF ANNUITY PAYMENTS

     The following discussion of the method for determining the amount of 
monthly annuity payments under a variable payment plan is intended to be read 
in conjunction with these sections of the prospectus for the Contracts:  
"Variable Payment Plans", p. 10, including "Description of Payment Plans", 
p. 10, "Amount of Annuity Payments", p. 10, and "Assumed Investment Rate", 
p. 10; "Dividends", p. 11; "Net Investment Factor", p. 9; and "Deductions", 
p. 13.

     AMOUNT OF ANNUITY PAYMENTS   The amount of the first annuity payment 
under a variable Payment Plan will be determined on the basis of the 
particular Payment Plan selected, the annuity payment rate and, for plans 
involving life contingencies, the Annuitant's adjusted age.  The amount of 
the first payment is the sum of the payments from each Division of the 
Account determined by applying the appropriate annuity payment rate to the 
product of the number of Accumulation Units in the Division on the effective 
date of the Payment Plan and the Accumulation Unit value for the Division on 
that date.  Annuity rates currently in use are based on the 1983 a Table with 
age adjustment.

     Variable annuity payments after the first will vary from month to month and
will depend upon the number and value of Annuity Units credited to the
Annuitant.  After the effective date of a Payment Plan a Contract will not share
in the divisible surplus of Northwestern Mutual Life.

     The number of Annuity Units in each Division is determined by dividing the
amount of the first annuity payment from the Division by the value of an Annuity
Unit on the effective date of the Payment Plan.  The number of Annuity Units
thus credited to the Annuitant in each Division remains constant throughout the
annuity period.  However, the value of Annuity Units in each Division will
fluctuate with the investment experience of the Division.

     The amount of each variable annuity payment after the first is the sum of
payments from each Division determined by multiplying this fixed number of
Annuity Units each month by the value of an Annuity Unit for the Division on (a)
the fifth valuation date prior to the payment due date if the payment due date
is a valuation date, or (b) the sixth valuation date prior to the payment due
date if the payment due date is not a valuation date.  To illustrate, if a
payment due date falls on a Friday, Saturday or Sunday, the amount of the
payment will normally be based upon the Annuity Unit value calculated on


                                   B-2
<PAGE>

the preceding Friday. The preceding Friday would be the fifth valuation date 
prior to the Friday due date, and the sixth valuation date prior to the 
Saturday or Sunday due dates.

     ANNUITY UNIT VALUE   The value of an Annuity Unit for each Division was
established at $1.00 as of the date operations began for that Division.  The
value of an Annuity Unit on any later date varies to reflect the investment
experience of the Division, the Assumed Investment Rate on which the annuity
rate tables are based, and the deduction for mortality rate and expense risks
assumed by Northwestern Mutual Life.

     The Annuity Unit value for each Division on any valuation date is 
determined by multiplying the Annuity Unit value on the immediately preceding 
valuation date by two factors:  (a) the net investment factor for the current 
period for the Division; and (b) an adjustment factor to neutralize the 
Assumed Investment Rate used in calculating the annuity rate tables.

     ILLUSTRATIONS OF VARIABLE ANNUITY PAYMENTS   To illustrate the manner in
which variable annuity payments are determined consider this example.  Item (4)
in the example shows the applicable monthly payment rate for an annuitant,
adjusted age 65, who has elected a life annuity Payment Plan with a certain
period of 10 years with an Assumed Investment Rate of 3-1/2% (Plan 2, as
described in the prospectus).

<TABLE>
<CAPTION>
     <C>    <S>                                                     <C>
     (1)    Assumed number of Accumulation Units in
            Balanced Division on
            maturity date . . . . . . . . . . . . . . . . . . . .   25,000

     (2)    Assumed Value of an Accumulation Unit in
            Balanced Division at
            maturity. . . . . . . . . . . . . . . . . . . . . . .   $2.000000

     (3)    Cash Value of Contract at maturity, (1) X (2) . . . .   $50,000

     (4)    Assumed applicable monthly payment rate per
            $1,000 from annuity rate table. . . . . . . . . . . .   $5.00

     (5)    Amount of first payment from
            Balanced Division,
            (3) X (4) divided by $1,000 . . . . . . . . . . . . .   $250.00

     (6)    Assumed Value of Annuity Unit in
            Balanced Division at maturity . . . . . . . . . . . .   $1.500000

     (7)    Number of Annuity Units credited in
            Balanced Division, (5) divided
            by (6). . . . . . . . . . . . . . . . . . . . . . . .   166.67
</TABLE>

The $50,000 value at maturity provides a first payment from the Balanced
Division of $250.00, and payments thereafter of the varying dollar value of
166.67 Annuity Units.  The amount of subsequent payments from the Balanced
Division is determined by multiplying 166.67 units by the value of an Annuity
Unit in the Balanced Division on the applicable valuation date.  For example, if
that unit value is $1.501000, the monthly payment from the Division will be
166.67 multiplied by $1.501000, or $250.17.


                                   B-3
<PAGE>

     However, the value of the Annuity Unit depends entirely on the investment
performance of the Division.  Thus in the example above, if the net investment
rate for the following month was less than the Assumed Investment Rate of
3-1/2%, the Annuity Unit would decline in value.  If the Annuity Unit value
declined to $1.499000 the succeeding monthly payment would then be 166.67 X
$1.499000, or $249.84.

     For the sake of simplicity the foregoing example assumes that all of the
Annuity Units are in the Balanced Division.  If there are Annuity Units in two
or more Divisions, the annuity payment from each Division is calculated
separately, in the manner illustrated, and the total monthly payment is the sum
of the payments from the Divisions.


                         VALUATION OF ASSETS OF THE ACCOUNT

     The value of Portfolio or  Fund shares held in each Division of the Account
at the time of each valuation is the redemption value of such shares at such
time.  If the right to redeem shares of a Portfolio or Fund has been suspended,
or payment of redemption value has been postponed, for the sole purpose of
computing annuity payments the shares held in the Account (and Annuity Units)
may be valued at fair value as determined in good faith by the Board of Trustees
of Northwestern Mutual Life.


                            TRANSFERABILITY RESTRICTIONS

     Ownership of a Contract cannot be changed or the Contract sold, assigned or
pledged as collateral for a loan, or for any other purpose, to any person other
than Northwestern Mutual Life; except, that if the Owner of the Contract is a
trustee of an employee trust qualified under the Code, or the custodian of a
custodial account treated as such, it may transfer the Contract to a successor
trustee or custodian.  In addition, the trustee or custodian, as well as the
employer under a qualified non-trusted pension plan, may assign the Contract to
an employee upon termination of employment.


                                      EXPERTS

     The financial statements of the Account as of December 31, 1998 and for
each of the two years in the period ended December 31, 1998 and of Northwestern
Mutual Life as of December 31, 1998 and 1997 and for each of the three years in
the period ended December 31, 1998 included in this Statement of Additional
Information have been so included in reliance on the reports of
PricewaterhouseCoopers LLP, independent accountants, given on the authority of
said firm as experts in auditing and accounting.  PricewaterhouseCoopers LLP
provides audit services for the Account.  The address of PricewaterhouseCoopers
LLP is 100 East Wisconsin Avenue, Suite 1500, Milwaukee, Wisconsin 53202.


                                  B-4
<PAGE>

ACCOUNT A FINANCIAL STATEMENTS
NML VARIABLE ANNUITY ACCOUNT A
Financial Statements
DECEMBER 31, 1998
STATEMENT OF ASSETS AND LIABILITIES
(IN THOUSANDS)
 
<TABLE>
<S>                                                 <C>         <C>
ASSETS
  Investments at Market Value:
    Northwestern Mutual Series Fund, Inc.
      Aggressive Growth Stock
       25,396 shares (cost $66,276)...............  $  87,973
      International Equity
       26,830 shares (cost $38,805)...............     44,995
      Growth Stock
       11,915 shares (cost $20,533)...............     26,774
      Growth and Income Stock
       22,438 shares (cost $31,395)...............     36,440
      Index 500 Stock
       43,592 shares (cost $75,957)...............    143,376
      Balanced
       146,262 shares (cost $214,781).............    325,287
      High Yield Bond
       9,922 shares (cost $10,685)................      9,287
      Select Bond
       20,792 shares (cost $24,420)...............     25,970
      Money Market
       26,910 shares (cost $26,910)...............  $  26,910   $ 727,012
                                                    ---------
Due from Sale of Fund Shares..................................      1,408
Due from Northwestern Mutual Life Insurance Company...........         22
                                                                ---------
Total Assets..................................................  $ 728,442
                                                                ---------
                                                                ---------
LIABILITIES
  Due to Participants.........................................  $   1,375
  Due to Northwestern Mutual Life Insurance Company...........      1,408
  Due on Purchase of Fund Shares..............................         26
                                                                ---------
      Total Liabilities.......................................      2,809
                                                                ---------
EQUITY (NOTE 8)
  Contracts Issued Prior to December 17, 1981.................  $  73,723
  Contracts Issued After December 16, 1981 and Prior to March
   31, 1995...................................................    558,227
  Contracts Issued On or After March 31, 1995:
  Front Load Version..........................................     15,243
  Back Load Version...........................................     78,440
                                                                ---------
      Total Equity............................................    725,633
                                                                ---------
      Total Liabilities and Equity............................  $ 728,442
                                                                ---------
                                                                ---------
</TABLE>
 
    The Accompanying Notes are an Integral Part of the Financial Statements


                                      B-5

<PAGE>

ACCOUNT A FINANCIAL STATEMENTS
NML VARIABLE ANNUITY ACCOUNT A
Statements of Operations and Changes in Equity
(IN THOUSANDS)
 
<TABLE>
<CAPTION>
                                                                      AGGRESSIVE GROWTH             INTERNATIONAL EQUITY
                                          COMBINED                     STOCK DIVISION                     DIVISION
                                -----------------------------   -----------------------------   -----------------------------
                                    YEAR                            YEAR                            YEAR
                                    ENDED        YEAR ENDED         ENDED        YEAR ENDED         ENDED        YEAR ENDED
                                DECEMBER 31,    DECEMBER 31,    DECEMBER 31,    DECEMBER 31,    DECEMBER 31,    DECEMBER 31,
                                    1998            1997            1998            1997            1998            1997
                                -------------   -------------   -------------   -------------   -------------   -------------
<S>                             <C>             <C>             <C>             <C>             <C>             <C>
INVESTMENT INCOME
Dividend Income...............    $ 34,233        $ 33,253        $ 3,294          $5,047         $ 2,855         $ 1,628
Annuity Rate and Expense
  Guarantees..................       8,067           7,047          1,049             979             591             580
                                -------------   -------------   -------------   -------------   -------------   -------------
Net Investment Income.........      26,166          26,206          2,245           4,068           2,264           1,048
                                -------------   -------------   -------------   -------------   -------------   -------------
REALIZED AND UNREALIZED GAIN
  ON INVESTMENTS
  Realized Gain on
    Investments...............      37,625          23,135          6,752           4,372           3,000           1,235
  Unrealized Appreciation
    (Depreciation) of
    Investments During the
    Period....................      36,250          56,364         (3,928)          1,563          (3,655)          2,446
                                -------------   -------------   -------------   -------------   -------------   -------------
  Net Gain (Loss) on
    Investments...............      73,875          79,499          2,824           5,935            (655)          3,681
                                -------------   -------------   -------------   -------------   -------------   -------------
  Increase in Equity Derived
    from Investment
    Activity..................     100,041         105,705          5,069          10,003           1,609           4,729
                                -------------   -------------   -------------   -------------   -------------   -------------
EQUITY TRANSACTIONS
  Contract Owners' Net
    Deposits..................      62,325          61,965         10,359          11,297           4,941           6,419
  Annuity Payments............      (1,306)         (1,047)           (41)            (40)            (32)            (25)
  Surrenders and Other
    (net).....................     (80,848)        (64,552)        (8,661)         (7,160)         (5,289)         (4,015)
  Transfers from Other
    Divisions or Sponsor......      95,967          63,046          8,930           8,697           5,056           6,734
  Transfers to Other Divisions
    or Sponsor................     (98,941)        (64,242)       (17,180)        (11,469)        (11,484)         (5,225)
                                -------------   -------------   -------------   -------------   -------------   -------------
Increase (Decrease) in Equity
  Derived from Equity
  Transactions................     (22,803)         (4,830)        (6,593)          1,325          (6,808)          3,888
                                -------------   -------------   -------------   -------------   -------------   -------------
Net Increase (Decrease) in
  Equity......................      77,238         100,875         (1,524)         11,328          (5,199)          8,617
EQUITY
  Beginning of Year...........     648,395         547,520         89,403          78,075          50,111          41,494
                                -------------   -------------   -------------   -------------   -------------   -------------
  End of Year.................    $725,633        $648,395        $87,879          $89,403        $44,912         $50,111
                                -------------   -------------   -------------   -------------   -------------   -------------
                                -------------   -------------   -------------   -------------   -------------   -------------
</TABLE>
 
    The Accompanying Notes are an Integral Part of the Financial Statements


                                       B-6

<PAGE>

NML VARIABLE ANNUITY ACCOUNT A
Statements of Operations and Changes in Equity
(IN THOUSANDS)
 
<TABLE>
<CAPTION>
                                                                    GROWTH & INCOME                  INDEX 500
                                   GROWTH STOCK DIVISION            STOCK DIVISION                STOCK DIVISION
                                ---------------------------   ---------------------------   ---------------------------
                                    YEAR                          YEAR                          YEAR
                                   ENDED        YEAR ENDED       ENDED        YEAR ENDED       ENDED        YEAR ENDED
                                DECEMBER 31,   DECEMBER 31,   DECEMBER 31,   DECEMBER 31,   DECEMBER 31,   DECEMBER 31,
                                    1998           1997           1998           1997           1998           1997
                                ------------   ------------   ------------   ------------   ------------   ------------
<S>                             <C>            <C>            <C>            <C>            <C>            <C>
INVESTMENT INCOME
Dividend Income...............    $    461       $    770       $    294       $  5,155       $  4,267       $  3,230
Annuity Rate and Expense
  Guarantees..................         263            151            353            214          1,404          1,062
                                ------------   ------------   ------------   ------------   ------------   ------------
Net Investment Income.........         198            619            (59)         4,941          2,863          2,168
                                ------------   ------------   ------------   ------------   ------------   ------------
REALIZED AND UNREALIZED GAIN
  ON INVESTMENTS
  Realized Gain on
    Investments...............       1,743            595          1,022            683          8,567          4,795
  Unrealized Appreciation
    (Depreciation) of
    Investments During the
    Period....................       2,872          2,039          4,954         (1,305)        18,919         19,474
                                ------------   ------------   ------------   ------------   ------------   ------------
  Net Gain (Loss) on
    Investments...............       4,615          2,634          5,976           (622)        27,486         24,269
                                ------------   ------------   ------------   ------------   ------------   ------------
  Increase in Equity Derived
    from Investment
    Activity..................       4,813          3,253          5,917          4,319         30,349         26,437
                                ------------   ------------   ------------   ------------   ------------   ------------
EQUITY TRANSACTIONS
  Contract Owners' Net
    Deposits..................       3,618          2,808          4,697          3,571         11,699          9,100
  Annuity Payments............          (4)            (2)           (55)           (35)          (411)          (334)
  Surrenders and Other
    (net).....................      (2,367)          (834)        (2,704)        (1,978)       (12,885)        (9,181)
  Transfers from Other
    Divisions or Sponsor......       7,949          4,394          9,679          6,598         17,648         10,885
  Transfers to Other Divisions
    or Sponsor................      (4,660)        (1,889)        (4,854)        (2,128)       (14,119)        (6,821)
                                ------------   ------------   ------------   ------------   ------------   ------------
Increase (Decrease) in Equity
  Derived from Equity
  Transactions................       4,536          4,477          6,763          6,028          1,932          3,649
                                ------------   ------------   ------------   ------------   ------------   ------------
Net Increase (Decrease) in
  Equity......................       9,349          7,730         12,680         10,347         32,281         30,086
EQUITY
  Beginning of Year...........      17,255          9,525         23,548         13,201        110,895         80,809
                                ------------   ------------   ------------   ------------   ------------   ------------
  End of Year.................    $ 26,604       $ 17,255       $ 36,228       $ 23,548       $143,176       $110,895
                                ------------   ------------   ------------   ------------   ------------   ------------
                                ------------   ------------   ------------   ------------   ------------   ------------
</TABLE>
 
    The Accompanying Notes are an Integral Part of the Financial Statements


                                       B-7

<PAGE>

NML VARIABLE ANNUITY ACCOUNT A
Statements of Operations and Changes in Equity
(IN THOUSANDS)
<TABLE>
<CAPTION>
                                     BALANCED DIVISION         HIGH YIELD BOND DIVISION        SELECT BOND DIVISION
                                ---------------------------   ---------------------------   ---------------------------
                                    YEAR                          YEAR                          YEAR
                                   ENDED        YEAR ENDED       ENDED        YEAR ENDED       ENDED        YEAR ENDED
                                DECEMBER 31,   DECEMBER 31,   DECEMBER 31,   DECEMBER 31,   DECEMBER 31,   DECEMBER 31,
                                    1998           1997           1998           1997           1998           1997
                                ------------   ------------   ------------   ------------   ------------   ------------
<S>                             <C>            <C>            <C>            <C>            <C>            <C>
INVESTMENT INCOME
Dividend Income...............    $ 19,089       $ 13,245       $    951       $  1,418       $  1,768       $  1,557
Annuity Rate and Expense
  Guarantees..................       3,750          3,458            113             84            277            274
                                ------------   ------------   ------------   ------------   ------------   ------------
Net Investment Income.........      15,339          9,787            838          1,334          1,491          1,283
                                ------------   ------------   ------------   ------------   ------------   ------------
REALIZED AND UNREALIZED GAIN
  ON INVESTMENTS
  Realized Gain on
    Investments...............      16,661         10,959           (220)           198            100            297
  Unrealized Appreciation
    (Depreciation) of
    Investments During the
    Period....................      18,160         32,245           (925)          (533)          (147)           435
                                ------------   ------------   ------------   ------------   ------------   ------------
  Net Gain (Loss) on
    Investments...............      34,821         43,204         (1,145)          (335)           (47)           732
                                ------------   ------------   ------------   ------------   ------------   ------------
  Increase in Equity Derived
    from Investment
    Activity..................      50,160         52,991           (307)           999          1,444          2,015
                                ------------   ------------   ------------   ------------   ------------   ------------
EQUITY TRANSACTIONS
  Contract Owners' Net
    Deposits..................      17,160         19,753          2,104          1,351          2,145          2,086
  Annuity Payments............        (662)          (515)            (5)            (3)           (59)           (50)
  Surrenders and Other
    (net).....................     (35,226)       (31,209)          (806)          (413)        (3,234)        (4,326)
  Transfers from Other
    Divisions or Sponsor......      10,851          6,095          4,761          3,537          3,443          2,638
  Transfers to Other Divisions
    or Sponsor................     (19,108)       (14,968)        (5,233)        (1,635)        (3,102)        (3,785)
                                ------------   ------------   ------------   ------------   ------------   ------------
Increase (Decrease) in Equity
  Derived from Equity
  Transactions................     (26,985)       (20,844)           821          2,837           (807)        (3,437)
                                ------------   ------------   ------------   ------------   ------------   ------------
Net Increase (Decrease) in
  Equity......................      23,175         32,148            514          3,836            637         (1,422)
EQUITY
  Beginning of Year...........     301,628        269,480          8,744          4,908         25,225         26,647
                                ------------   ------------   ------------   ------------   ------------   ------------
  End of Year.................    $324,803       $301,628       $  9,258       $  8,744       $ 25,862       $ 25,225
                                ------------   ------------   ------------   ------------   ------------   ------------
                                ------------   ------------   ------------   ------------   ------------   ------------
 
<CAPTION>
 
                                   MONEY MARKET DIVISION
                                ---------------------------
 
                                    YEAR
                                   ENDED        YEAR ENDED
                                DECEMBER 31,   DECEMBER 31,
                                    1998           1997
                                ------------   ------------
<S>                             <C>            <C>
INVESTMENT INCOME
Dividend Income...............    $  1,254       $  1,203
Annuity Rate and Expense
  Guarantees..................         267            245
                                ------------   ------------
Net Investment Income.........         987            958
                                ------------   ------------
REALIZED AND UNREALIZED GAIN
  ON INVESTMENTS
  Realized Gain on
    Investments...............          --             --
  Unrealized Appreciation
    (Depreciation) of
    Investments During the
    Period....................          --             --
                                ------------   ------------
  Net Gain (Loss) on
    Investments...............          --             --
                                ------------   ------------
  Increase in Equity Derived
    from Investment
    Activity..................         987            958
                                ------------   ------------
EQUITY TRANSACTIONS
  Contract Owners' Net
    Deposits..................       5,602          5,580
  Annuity Payments............         (37)           (43)
  Surrenders and Other
    (net).....................      (9,676)        (5,436)
  Transfers from Other
    Divisions or Sponsor......      27,650         13,468
  Transfers to Other Divisions
    or Sponsor................     (19,201)       (16,322)
                                ------------   ------------
Increase (Decrease) in Equity
  Derived from Equity
  Transactions................       4,338         (2,753)
                                ------------   ------------
Net Increase (Decrease) in
  Equity......................       5,325         (1,795)
EQUITY
  Beginning of Year...........      21,586         23,381
                                ------------   ------------
  End of Year.................    $ 26,911       $ 21,586
                                ------------   ------------
                                ------------   ------------
</TABLE>
 
    The Accompanying Notes are an Integral Part of the Financial Statements


                                       B-8

<PAGE>

NOTES TO FINANCIAL STATEMENTS
NML VARIABLE ANNUITY ACCOUNT A
Notes to Financial Statements
DECEMBER 31, 1998
 
NOTE 1 -- NML Variable Annuity Account A (the "Account") is a segregated asset
account of The Northwestern Mutual Life Insurance Company ("Northwestern Mutual"
or "Sponsor") used to fund variable annuity contracts ("contracts") for HR-10
and corporate pension and profit-sharing plans which qualify for special tax
treatment under the Internal Revenue Code. Beginning March 31, 1995, two
versions of the contract are offered: Front Load contracts with a sales charge
up to 4% of purchase payments and Back Load contracts with a withdrawal charge
of 0-8%.
 
NOTE 2 -- The preparation of the financial statements in conformity with
generally accepted accounting principles requires management to make estimates
and assumptions that affect the reported amounts of assets and liabilities and
disclosure of contingent assets and liabilities at the date of the financial
statements and the reported amounts of revenues and expenses during the
reporting period. Actual results could differ from those estimates. Principal
accounting policies are summarized below.
 
NOTE 3 -- All assets of each Division of the Account are invested in shares of
the corresponding Portfolio of Northwestern Mutual Series Fund, Inc. (the
"Fund"). The shares are valued at the Fund's offering and redemption price per
share.
 
The Fund is an open-end investment company registered under the Investment
Company Act of 1940.
 
NOTE 4 -- Annuity reserves are based on published annuity tables with age
adjustment and benefit payments which reflect actual investment experience. For
variable payment plans issued prior to January 1, 1974, annuity reserves are
based on the 1955 American Annuity Table with assumed interest rates of 3% or
5%. For variable payment plans issued on or after January 1, 1974 and before
January 1, 1985, annuity reserves are based on the 1971 Individual Annuity Table
with assumed interest rates of 3 1/2% or 5%. For variable payment plans issued
on or after January 1, 1985, annuity reserves are based on the 1983 Table a with
assumed interest rates of 3 1/2% or 5%.
 
NOTE 5 -- Dividend income from the Fund is recorded on the record date of the
dividends. Transactions in Fund shares are accounted for on the trade date. The
basis for determining cost on sale of Fund shares is identified cost. Purchases
and sales of Fund shares for the year ended December 31, 1998 by each Division
are shown below:
 
<TABLE>
<CAPTION>
                                     PURCHASES          SALES
                                  ---------------  ---------------
<S>                               <C>              <C>
Aggressive Growth Division......  $    10,360,035  $    14,639,276
International Equity Division...        6,698,885       11,198,223
Growth Stock Division...........        9,097,053        4,198,359
Growth & Income Stock
Division........................       10,667,937        3,780,324
Index 500 Stock Division........       18,355,852       13,607,476
Balanced Division...............       28,049,864       40,333,474
High Yield Bond Division........        5,801,403        4,113,088
Select Bond Division............        5,372,185        4,608,524
Money Market Division...........       24,597,925       19,273,286
</TABLE>
 
NOTE 6 -- A deduction for annuity rate and expense guarantees is determined
daily and paid to Northwestern Mutual as compensation for assuming the risk that
annuity payments will continue for longer periods than anticipated because the
annuitants as a group live longer than expected, and the risk that the charges
made by Northwestern Mutual may be insufficient to cover the actual costs
incurred in connection with the contracts.
 
For contracts issued on or after March 31, 1995, for the Front Load version and
the Back Load version, the deduction for annuity rate and expense guarantees is
determined daily at annual rates of 4/10 of 1% and 1 1/4%, respectively, of the
net assets of each Division attributable to these contracts and is paid to
Northwestern Mutual. For these contracts, the rates may be increased or
decreased by the Board of Trustees of Northwestern Mutual not to exceed 3/4 of
1% and 1 1/2%, respectively.
 
For contracts issued after December 16, 1981 and prior to March 31, 1995, the
deduction is at an annual rate of 1 1/4% of the net assets of each division
attributable to these contracts. For these contracts, the rate may be increased
or decreased by the Board of Trustees of Northwestern Mutual not to exceed a
1 1/2% annual rate.
 
For contracts issued prior to December 17, 1981, the deduction is at an annual
rate of 3/4 of 1% of the net assets of each Division attributable to these
contracts. For these contracts, the rate may be increased or decreased by the
Board of Trustees of Northwestern Mutual not to exceed a 1% annual rate.
 
Since 1995, Northwestern Mutual has paid a dividend to certain contracts. The
dividend is re-invested in the Account and has been reflected as a Contract
Owners' Net Deposit in the accompanying financial statements.
 
NOTE 7 -- Northwestern Mutual is taxed as a "life insurance company" under the
Internal Revenue Code and the operations of the Account form a part of and are
taxed with those of Northwestern Mutual. Under current law, no federal income
taxes are payable with respect to the Account. Accordingly, no provision for any
such liability has been made.


                                       B-9
<PAGE>

NML VARIABLE ANNUITY ACCOUNT A
Notes to Financial Statements
(IN THOUSANDS)
DECEMBER 31, 1998
NOTE 8 -- Equity Values by Division are shown below:
 
<TABLE>
<CAPTION>
                                                                                               CONTRACTS ISSUED:
                                                     CONTRACTS ISSUED:                    AFTER DECEMBER 16, 1981 AND
                                                 PRIOR TO DECEMBER 17, 1981                 PRIOR TO MARCH 31, 1995
                                          ----------------------------------------  ----------------------------------------
                                           ACCUMULATION       UNITS                  ACCUMULATION      UNITS
DIVISION                                    UNIT VALUE     OUTSTANDING    EQUITY      UNIT VALUE    OUTSTANDING     EQUITY
- ----------------------------------------  --------------  -------------  ---------  --------------  ------------  ----------
<S>                                       <C>             <C>            <C>        <C>             <C>           <C>
Aggressive Growth Stock.................   $   3.964849          480     $  1,901    $   3.808330       18,213    $  69,362
International Equity....................       1.947470          648        1,262        1.893030       19,262       36,463
Growth Stock............................       2.549324          248          631        2.490522        7,216       17,971
Growth and Income.......................       2.437983          310          756        2.381813       10,867       25,883
Index 500 Stock.........................       4.202480        7,343       30,860        4.036666       21,468       86,659
Balanced................................       7.372322        3,014       22,217        6.771353       40,488      274,158
High Yield Bond.........................       1.582307          183          290        1.545816        3,975        6,144
Select Bond.............................       7.718724          900        6,946        7.088069        2,172       15,394
Money Market............................       2.646458        1,723        4,561        2.430915        6,700       16,286
 
  Equity................................                                   69,424                                   548,320
                                                                         ---------                                ----------
  Annuity Reserves......................                                    4,299                                     9,907
                                                                         ---------                                ----------
  Total Equity..........................                                 $ 73,723                                 $ 558,227
                                                                         ---------                                ----------
                                                                         ---------                                ----------
</TABLE>
 
<TABLE>
<CAPTION>
                                                       CONTRACTS ISSUED:                         CONTRACTS ISSUED:
                                                   ON OR AFTER MARCH 31, 1995                ON OR AFTER MARCH 31, 1995
                                                       FRONT LOAD VERSION                        BACK LOAD VERSION
                                            ----------------------------------------  ----------------------------------------
                                             ACCUMULATION       UNITS                  ACCUMULATION       UNITS
DIVISION                                      UNIT VALUE     OUTSTANDING    EQUITY      UNIT VALUE     OUTSTANDING    EQUITY
- ------------------------------------------  --------------  -------------  ---------  --------------  -------------  ---------
<S>                                         <C>             <C>            <C>        <C>             <C>            <C>
Aggressive Growth Stock...................   $   1.858751        1,195     $  2,221    $   3.808330        3,703     $ 14,105
International Equity......................       1.604722          669        1,074        1.893030        3,028        5,733
Growth Stock..............................       2.375383          448        1,064        2.490522        2,761        6,877
Growth and Income Stock...................       2.270962          737        1,673        2.381813        3,046        7,256
Index 500 Stock...........................       2.597374        1,058        2,748        4.036666        4,504       18,182
Balanced..................................       1.912247        1,769        3,383        6.771353        2,565       17,370
High Yield Bond...........................       1.495835          400          599        1.545816        1,401        2,165
Select Bond...............................       1.350384          160          216        7.088069          368        2,611
Money Market..............................       1.203067        1,564        1,882        2.430915        1,515        3,683
 
  Equity..................................                                   14,860                                    77,982
                                                                           ---------                                 ---------
  Annuity Reserves........................                                      383                                       458
                                                                           ---------                                 ---------
  Total Equity............................                                 $ 15,243                                  $ 78,440
                                                                           ---------                                 ---------
                                                                           ---------                                 ---------
</TABLE>


                                      B-10
<PAGE>

ACCOUNTANTS' REPORT

                           [LOGO]
 
REPORT OF INDEPENDENT ACCOUNTANTS
 
To The Northwestern Mutual Life Insurance Company and
Contract Owners NML Variable Annuity Account A
 
In our opinion, the accompanying combined statement of assets and liabilities
and the related combined and separate statements of operations and changes in
equity present fairly, in all material respects, the financial position of NML
Variable Annuity Account A and the Aggressive Growth Stock Division,
International Equity Division, Growth Stock Division, Growth and Income Stock
Division, Index 500 Stock Division, Balanced Division, High Yield Bond Division,
Select Bond Division and the Money Market Division thereof at December 31, 1998,
the results of each of their operations and the changes in each of their equity
for each of the two years in the period ended December 31, 1998 in conformity
with generally accepted accounting principles. These financial statements are
the responsibility of The Northwestern Mutual Life Insurance Company's
management; our responsibility is to express an opinion on these financial
statements based on our audits. We conducted our audits of these financial
statements in accordance with generally accepted auditing standards which
require that we plan and perform the audit to obtain reasonable assurance about
whether the financial statements are free of material misstatement. An audit
includes examining, on a test basis, evidence supporting the amounts and
disclosures in the financial statements, assessing the accounting principles
used and significant estimates made by management, and evaluating the overall
financial statement presentation. We believe that our audits, which included
direct confirmation of the number of shares owned at December 31, 1998 with
Northwestern Mutual Series Fund, Inc., provide a reasonable basis for the
opinion expressed above.
 
                        [SIGNATURE]
 
Milwaukee, Wisconsin
January 25, 1999


                                      B-11
<PAGE>

                 THE NORTHWESTERN MUTUAL LIFE INSURANCE COMPANY
 
THE NORTHWESTERN MUTUAL LIFE INSURANCE COMPANY
 
CONSOLIDATED STATEMENT OF FINANCIAL POSITION
 
(IN MILLIONS)
 
The following financial statements of Northwestern Mutual should be considered
only as bearing upon the ability of Northwestern Mutual Life to meet its
obligations under the Policies.
 
<TABLE>
<CAPTION>
                                                        DECEMBER 31,
                                                    ---------------------
                                                      1998        1997
                                                    ---------   ---------
<S>                                                 <C>         <C>
ASSETS
    Bonds.........................................  $  34,888   $  32,359
    Common and preferred stocks...................      6,576       6,524
    Mortgage loans................................     12,250      10,835
    Real estate...................................      1,481       1,372
    Policy loans..................................      7,580       7,163
    Other investments.............................      1,839       2,026
    Cash and temporary investments................      1,275         572
    Due and accrued investment income.............        827         795
    Other assets..................................      1,313       1,275
    Separate account assets.......................      9,966       8,160
                                                    ---------   ---------
        Total assets..............................  $  77,995   $  71,081
                                                    ---------   ---------
                                                    ---------   ---------
LIABILITIES AND SURPLUS
    Reserves for policy benefits..................  $  51,815   $  47,343
    Policy benefit and premium deposits...........      1,709       1,624
    Policyowner dividends payable.................      2,870       2,640
    Interest maintenance reserve..................        606         461
    Asset valuation reserve.......................      1,994       1,974
    Income taxes payable..........................      1,161       1,043
    Other liabilities.............................      3,133       3,735
    Separate account liabilities..................      9,966       8,160
                                                    ---------   ---------
        Total liabilities.........................     73,254      66,980
    Surplus.......................................      4,741       4,101
                                                    ---------   ---------
        Total liabilities and surplus.............  $  77,995   $  71,081
                                                    ---------   ---------
                                                    ---------   ---------
</TABLE>
 
   The accompanying notes are an integral part of these financial statements.
 

                                       B-12

<PAGE>

                 THE NORTHWESTERN MUTUAL LIFE INSURANCE COMPANY
 
THE NORTHWESTERN MUTUAL LIFE INSURANCE COMPANY
 
CONSOLIDATED STATEMENT OF OPERATIONS
 
(IN MILLIONS)
 
<TABLE>
<CAPTION>
                                                     FOR THE YEAR ENDED DECEMBER 31,
                                                    ---------------------------------
                                                      1998        1997        1996
                                                    ---------   ---------   ---------
<S>                                                 <C>         <C>         <C>
REVENUE
    Premium income................................  $  8,021    $  7,294    $  6,667
    Net investment income.........................     4,536       4,171       3,836
    Other income..................................       922         861         759
                                                    ---------   ---------   ---------
        Total revenue.............................    13,479      12,326      11,262
                                                    ---------   ---------   ---------
BENEFITS AND EXPENSES
    Benefit payments to policyowners and
     beneficiaries................................     3,602       3,329       2,921
    Net additions to policy benefit reserves......     4,521       4,026       3,701
    Net transfers to separate accounts............       564         566         579
                                                    ---------   ---------   ---------
        Total benefits............................     8,687       7,921       7,201
    Operating expenses............................     1,297       1,138       1,043
                                                    ---------   ---------   ---------
        Total benefits and expenses...............     9,984       9,059       8,244
                                                    ---------   ---------   ---------
Gain from operations before dividends and taxes...     3,495       3,267       3,018
Policyowner dividends.............................     2,869       2,636       2,341
                                                    ---------   ---------   ---------
Gain from operations before taxes.................       626         631         677
Income tax expense................................       301         356         452
                                                    ---------   ---------   ---------
Net gain from operations..........................       325         275         225
Net realized capital gains........................       484         414         395
                                                    ---------   ---------   ---------
        Net income................................  $    809    $    689    $    620
                                                    ---------   ---------   ---------
                                                    ---------   ---------   ---------
</TABLE>
 
   The accompanying notes are an integral part of these financial statements.


                                       B-13

<PAGE>

                 THE NORTHWESTERN MUTUAL LIFE INSURANCE COMPANY
 
THE NORTHWESTERN MUTUAL LIFE INSURANCE COMPANY
 
CONSOLIDATED STATEMENT OF CHANGES IN SURPLUS
 
(IN MILLIONS)
 
<TABLE>
<CAPTION>
                                                      FOR THE YEAR ENDED DECEMBER 31,
                                                      -------------------------------
                                                       1998        1997        1996
                                                      -------     -------     -------
<S>                                                   <C>         <C>         <C>
BEGINNING OF YEAR BALANCE.........................    $4,101      $3,515      $2,786
  Net income......................................       809         689         620
  Increase (decrease) in net unrealized gains.....      (147)        576         295
  Increase in investment reserves.................       (20)       (526)       (176)
  Other, net......................................        (2)       (153)        (10)
                                                      -------     -------     -------
  Net increase in surplus.........................       640         586         729
                                                      -------     -------     -------
END OF YEAR BALANCE...............................    $4,741      $4,101      $3,515
                                                      -------     -------     -------
                                                      -------     -------     -------
</TABLE>
 
   The accompanying notes are an integral part of these financial statements.


                                       B-14

<PAGE>

                 THE NORTHWESTERN MUTUAL LIFE INSURANCE COMPANY
 
THE NORTHWESTERN MUTUAL LIFE INSURANCE COMPANY
 
CONSOLIDATED STATEMENT OF CASH FLOWS
 
(IN MILLIONS)
 
<TABLE>
<CAPTION>
                                                       FOR THE YEAR ENDED DECEMBER 31,
                                                      ----------------------------------
                                                        1998         1997         1996
                                                      --------     --------     --------
<S>                                                   <C>          <C>          <C>
CASH FLOWS FROM OPERATING ACTIVITIES
  Insurance and annuity premiums..................    $ 8,876      $ 8,093      $ 7,361
  Investment income received......................      4,216        3,928        3,634
  Disbursement of policy loans, net of
   repayments.....................................       (416)        (360)        (326)
  Benefits paid to policyowners and
   beneficiaries..................................     (3,572)      (3,316)      (2,912)
  Net transfers to separate accounts..............       (564)        (565)        (579)
  Policyowner dividends paid......................     (2,639)      (2,347)      (2,105)
  Operating expenses and taxes....................     (1,749)      (1,722)      (1,663)
  Other, net......................................        (83)         124          (59)
                                                      --------     --------     --------
    NET CASH PROVIDED BY OPERATING ACTIVITIES.....      4,069        3,835        3,351
                                                      --------     --------     --------
CASH FLOWS FROM INVESTING ACTIVITIES
  PROCEEDS FROM INVESTMENTS SOLD OR MATURED
    Bonds.........................................     28,720       38,284       31,942
    Common and preferred stocks...................     10,359        9,057        4,570
    Mortgage loans................................      1,737        1,012        1,253
    Real estate...................................        159          302          178
    Other investments.............................        768          398          316
                                                      --------     --------     --------
                                                       41,743       49,053       38,259
                                                      --------     --------     --------
  COST OF INVESTMENTS ACQUIRED
    Bonds.........................................     30,873       41,169       35,342
    Common and preferred stocks...................      9,642        9,848        4,463
    Mortgage loans................................      3,135        2,309        2,455
    Real estate...................................        268          202          125
    Other investments.............................        567          359          255
                                                      --------     --------     --------
                                                       44,485       53,887       42,640
                                                      --------     --------     --------
  NET INCREASE (DECREASE) IN SECURITIES LENDING
   AND OTHER......................................       (624)         440        1,617
                                                      --------     --------     --------
    NET CASH USED IN INVESTING ACTIVITIES.........     (3,366)      (4,394)      (2,764)
                                                      --------     --------     --------
NET INCREASE (DECREASE) IN CASH AND TEMPORARY
 INVESTMENTS......................................        703         (559)         587
CASH AND TEMPORARY INVESTMENTS, BEGINNING OF
 YEAR.............................................        572        1,131          544
                                                      --------     --------     --------
CASH AND TEMPORARY INVESTMENTS, END OF YEAR.......    $ 1,275      $   572      $ 1,131
                                                      --------     --------     --------
                                                      --------     --------     --------
</TABLE>
 
   The accompanying notes are an integral part of these financial statements.


                                       B-15

<PAGE>

                 THE NORTHWESTERN MUTUAL LIFE INSURANCE COMPANY
 
THE NORTHWESTERN MUTUAL LIFE INSURANCE COMPANY
 
NOTES TO CONSOLIDATED STATUTORY FINANCIAL STATEMENTS
 
DECEMBER 31, 1998, 1997 AND 1996
 
1. PRINCIPAL ACCOUNTING POLICIES
 
The accompanying consolidated statutory financial statements include the
accounts of The Northwestern Mutual Life Insurance Company ("Company") and its
wholly-owned life insurance subsidiary, Northwestern Long Term Care Insurance
Company ("Subsidiary"). The Company and its Subsidiary offer life, annuity,
disability income and long term care products to the personal, business, estate
and tax-qualified markets.
 
The consolidated financial statements have been prepared using accounting
policies prescribed or permitted by the Office of the Commissioner of Insurance
of the State of Wisconsin ("statutory basis of accounting").
 
In 1998, the National Association of Insurance Commissioners ("NAIC") adopted
the Codification of Statutory Accounting Principles, which will replace the
current Accounting Practices and Procedures manual as the NAIC's primary
guidance on statutory accounting. The NAIC is now considering amendments to the
codification guidance that would also be effective upon its planned
implementation effective January 1, 2001. It is expected that the Office of the
Commissioner of Insurance of the State of Wisconsin ("OCI") will adopt the
codification, but it is not known whether the OCI will make any changes to that
guidance. The potential effect of the codification on the Company will depend
upon the guidance adopted by the OCI.
 
Financial statements prepared on the statutory basis of accounting vary from
financial statements prepared on the basis of Generally Accepted Accounting
Principles ("GAAP") primarily because on a GAAP basis (1) policy acquisition
costs are deferred and amortized, (2) investment valuations and insurance
reserves are based on different assumptions, (3) funds received under
deposit-type contracts are not reported as premium revenue, and (4) deferred
taxes are provided for temporary differences between book and tax basis of
certain assets and liabilities. The effects on the financial statements of the
differences between the statutory basis of accounting and GAAP are material to
the Company.
 
The preparation of financial statements in conformity with the statutory basis
of accounting requires management to make estimates and assumptions that affect
the reported amounts of assets and liabilities at the date of the financial
statements and the reported amounts of revenues and expenses during the
reporting period. Actual future results could differ from these estimates.
 
INVESTMENTS
 
The Company's investments are valued on the following bases:
 
<TABLE>
<S>                             <C>  <C>
Bonds                           --   Amortized cost using the interest method; loan-backed and
                                     structured securities are amortized using estimated
                                     prepayment rates and, generally, the prospective adjustment
                                     method
Common and preferred stocks     --   Common stocks are carried at fair value, preferred stocks
                                     are generally carried at cost, and unconsolidated
                                     subsidiaries are recorded using the equity method
Mortgage loans                  --   Amortized cost
Real estate                     --   Lower of cost, less depreciation and encumbrances, or
                                     estimated net realizable value
Policy loans                    --   Unpaid principal balance, which approximates fair value
Other investments               --   Consists primarily of joint venture investments which are
                                     valued at equity in ventures' net assets
Cash and temporary investments  --   Amortized cost, which approximates fair value
</TABLE>


                                       B-16

<PAGE>

                 THE NORTHWESTERN MUTUAL LIFE INSURANCE COMPANY
 
THE NORTHWESTERN MUTUAL LIFE INSURANCE COMPANY
 
NOTES TO CONSOLIDATED STATUTORY FINANCIAL STATEMENTS
 
DECEMBER 31, 1998, 1997 AND 1996
 
TEMPORARY INVESTMENTS
 
Temporary investments consist of debt securities that have maturities of one
year or less at acquisition.
 
NET INVESTMENT INCOME
 
Net investment income includes interest and dividends received or due and
accrued on debt securities and stocks, equity in unconsolidated subsidiaries'
earnings and the Company's share of joint venture income. Net investment income
is reduced by investment management expenses, real estate depreciation,
depletion related to energy assets and costs associated with securities lending.
 
INTEREST MAINTENANCE RESERVE
 
The Company is required to maintain an interest maintenance reserve ("IMR"). The
IMR is used to defer realized gains and losses, net of tax, on fixed income
investments resulting from changes in interest rates. Net realized gains and
losses deferred to the IMR are amortized into investment income over the
approximate remaining term to maturity of the investment sold.
 
INVESTMENT RESERVES
 
The Company is required to maintain an asset valuation reserve ("AVR"). The AVR
establishes a general reserve for invested asset valuation using a formula
prescribed by state regulations. The AVR is designed to stabilize surplus
against potential declines in the value of investments. In addition, the Company
maintained a $200 million voluntary investment reserve at December 31, 1998 and
1997 to absorb potential investment losses exceeding those considered by the AVR
formula. Increases or decreases in these investment reserves are recorded
directly to surplus.
 
SEPARATE ACCOUNTS
 
Separate account assets and related policy liabilities represent the segregation
of funds deposited by "variable" life insurance and annuity policyowners.
Policyowners bear the investment performance risk associated with variable
products. Separate account assets are invested at the direction of the
policyowner in a variety of Company-managed mutual funds. Variable product
policyowners also have the option to invest in a fixed interest rate annuity in
the general account of the Company. Separate account assets are reported at fair
value.
 
PREMIUM REVENUE AND OPERATING EXPENSES
 
Life insurance premiums are recognized as revenue at the beginning of each
policy year. Annuity and disability income premiums are recognized when received
by the Company. Operating expenses, including costs of acquiring new policies,
are charged to operations as incurred.
 
OTHER INCOME
 
Other income includes considerations on supplementary contracts, ceded
reinsurance expense allowances and miscellaneous policy charges.
 

                                       B-17

<PAGE>

                 THE NORTHWESTERN MUTUAL LIFE INSURANCE COMPANY
 
THE NORTHWESTERN MUTUAL LIFE INSURANCE COMPANY
 
NOTES TO CONSOLIDATED STATUTORY FINANCIAL STATEMENTS
 
DECEMBER 31, 1998, 1997 AND 1996
 
BENEFIT PAYMENTS TO POLICYOWNERS AND BENEFICIARIES
 
Benefit payments to policyowners and beneficiaries include death, surrender and
disability benefits, matured endowments and supplementary contract payments.
 
RESERVES FOR POLICY BENEFITS
 
Reserves for policy benefits are determined using actuarial estimates based on
mortality and morbidity experience tables and valuation interest rates
prescribed by the Office of the Commissioner of Insurance of the State of
Wisconsin. See Note 3.
 
POLICYOWNER DIVIDENDS
 
Almost all life insurance policies, and certain annuity and disability income
policies, issued by the Company are participating. Annually, the Company's Board
of Trustees approves dividends payable on participating policies in the
following fiscal year, which are accrued and charged to operations when
approved.
 
RECLASSIFICATION
 
Certain financial statement balances for 1997 and 1996 have been reclassified to
conform to the current year presentation.
 
2. INVESTMENTS
 
DEBT SECURITIES
 
Debt securities consist of all bonds and fixed-maturity preferred stocks. The
estimated fair values of debt securities are based upon quoted market prices, if
available. For securities not actively traded, fair values are estimated using
independent pricing services or internally developed pricing models. The Company
records unrealized losses for debt securities considered impaired.
 

                                       B-18

<PAGE>

                 THE NORTHWESTERN MUTUAL LIFE INSURANCE COMPANY
 
THE NORTHWESTERN MUTUAL LIFE INSURANCE COMPANY
 
NOTES TO CONSOLIDATED STATUTORY FINANCIAL STATEMENTS
 
DECEMBER 31, 1998, 1997 AND 1996
 
Statement value, which principally represents amortized cost, and estimated fair
value of the Company's debt securities at December 31, 1998 and 1997 were as
follows:
<TABLE>
<CAPTION>
                                                                RECONCILIATION TO ESTIMATED FAIR VALUE
                                                                ---------------------------------------
                                                                   GROSS          GROSS       ESTIMATED
                                                    STATEMENT    UNREALIZED     UNREALIZED      FAIR
DECEMBER 31, 1998                                     VALUE     APPRECIATION   DEPRECIATION     VALUE
- --------------------------------------------------  ---------   ------------   ------------   ---------
                                                                       (IN MILLIONS)
<S>                                                 <C>         <C>            <C>            <C>
US Government and political obligations...........  $ 3,904       $  461          $ (11)      $ 4,354
Mortgage-backed securities........................    7,357          280            (15)        7,622
Corporate and other debt securities...............   23,627        1,240           (382)       24,485
                                                    ---------   ------------     ------       ---------
                                                     34,888        1,981           (408)       36,461
Preferred stocks..................................      189            4             (1)          192
                                                    ---------   ------------     ------       ---------
Total.............................................  $35,077       $1,985          $(409)      $36,653
                                                    ---------   ------------     ------       ---------
                                                    ---------   ------------     ------       ---------
 
<CAPTION>
 
                                                                RECONCILIATION TO ESTIMATED FAIR VALUE
                                                                ---------------------------------------
                                                                   GROSS          GROSS       ESTIMATED
                                                    STATEMENT    UNREALIZED     UNREALIZED      FAIR
DECEMBER 31, 1997                                     VALUE     APPRECIATION   DEPRECIATION     VALUE
- --------------------------------------------------  ---------   ------------   ------------   ---------
                                                                       (IN MILLIONS)
<S>                                                 <C>         <C>            <C>            <C>
US Government and political obligations...........  $ 3,695       $  336          $  (3)      $ 4,028
Mortgage-backed securities........................    7,015          264             (4)        7,275
Corporate and other debt securities...............   21,649        1,098           (208)       22,539
                                                    ---------   ------------     ------       ---------
                                                     32,359        1,698           (215)       33,842
Preferred stocks..................................      167            4             (2)          169
                                                    ---------   ------------     ------       ---------
Total.............................................  $32,526       $1,702          $(217)      $34,011
                                                    ---------   ------------     ------       ---------
                                                    ---------   ------------     ------       ---------
</TABLE>
 
The statement value of debt securities by contractual maturity at December 31,
1998 and 1997 is shown below. Expected maturities may differ from contractual
maturities because borrowers may have the right to call or prepay obligations
with or without call or prepayment penalties.
 
<TABLE>
<CAPTION>
                                                    DECEMBER 31,   DECEMBER 31,
                                                        1998           1997
                                                    ------------   ------------
                                                           (IN MILLIONS)
<S>                                                 <C>            <C>
Due in one year or less...........................    $   655        $   605
Due after one year through five years.............      5,031          4,878
Due after five years through ten years............     10,286          9,760
Due after ten years...............................     11,748         10,268
                                                    ------------   ------------
                                                       27,720         25,511
Mortgage-backed securities........................      7,357          7,015
                                                    ------------   ------------
                                                      $35,077        $32,526
                                                    ------------   ------------
                                                    ------------   ------------
</TABLE>
 
STOCKS
 
The estimated fair values of common and perpetual preferred stocks are based
upon quoted market prices, if available. For securities not actively traded,
fair values are estimated using independent pricing services or internally
developed pricing models.


                                       B-19

<PAGE>

                 THE NORTHWESTERN MUTUAL LIFE INSURANCE COMPANY
 
THE NORTHWESTERN MUTUAL LIFE INSURANCE COMPANY
 
NOTES TO CONSOLIDATED STATUTORY FINANCIAL STATEMENTS
 
DECEMBER 31, 1998, 1997 AND 1996
 
The adjusted cost of common and preferred stock held by the Company at December
31, 1998 and 1997 was $4.8 billion and $5.0 billion, respectively.
 
MORTGAGE LOANS AND REAL ESTATE
 
Mortgage loans are collateralized by properties located throughout the United
States and Canada. The Company attempts to minimize mortgage loan investment
risk by diversification of geographic locations and types of collateral
properties.
 
The fair value of mortgage loans as of December 31, 1998 and 1997 was
approximately $12.9 billion and $11.5 billion, respectively. The fair value of
the mortgage loan portfolio is estimated by discounting the future estimated
cash flows using current interest rates of debt securities with similar credit
risk and maturities, or utilizing net realizable values.
 
At December 31, 1998 and 1997, real estate includes $61 million acquired through
foreclosure at each date and $120 million and $124 million, respectively, of
home office real estate. In 1998, 1997 and 1996, the Company recorded unrealized
losses of $5 million, $2 million and $43 million, respectively, for the excess
of statement value over fair value of certain real estate investments and
mortgage loans.
 
REALIZED GAINS AND LOSSES
 
Realized investment gains and losses for the years ended December 31, 1998, 1997
and 1996 were as follows:
 
<TABLE>
<CAPTION>
                                      FOR THE YEAR ENDED               FOR THE YEAR ENDED               FOR THE YEAR ENDED
                                      DECEMBER 31, 1998                DECEMBER 31, 1997                DECEMBER 31, 1996
                                ------------------------------   ------------------------------   ------------------------------
                                                        NET                              NET                              NET
                                                      REALIZED                         REALIZED                         REALIZED
                                REALIZED   REALIZED    GAINS     REALIZED   REALIZED    GAINS     REALIZED   REALIZED    GAINS
                                 GAINS      LOSSES    (LOSSES)    GAINS      LOSSES    (LOSSES)    GAINS      LOSSES    (LOSSES)
                                --------   --------   --------   --------   --------   --------   --------   --------   --------
                                                                         (IN MILLIONS)
<S>                             <C>        <C>        <C>        <C>        <C>        <C>        <C>        <C>        <C>
Bonds.........................  $   514     $ (231)    $  283    $   518     $ (269)    $ 249     $   396     $ (383)    $   13
Common and preferred stocks...      885       (240)       645        533       (150)      383         580       (115)       465
Mortgage loans................       18        (11)         7         14        (14)        -           2        (15)       (13)
Real estate...................       41          -         41        100         (2)       98          36          -         36
Other investments.............      330       (267)        63        338       (105)      233         204        (51)       153
                                --------   --------   --------   --------   --------   --------   --------   --------   --------
                                  1,788       (749)     1,039      1,503       (540)      963       1,218       (564)       654
                                --------   --------   --------   --------   --------   --------   --------   --------   --------
Less: Capital gains taxes.....                            358                             340                               224
Less: IMR deferrals...........                            197                             209                                35
                                                      --------                         --------                         --------
Net realized capital gains....                         $  484                           $ 414                            $  395
                                                      --------                         --------                         --------
                                                      --------                         --------                         --------
</TABLE>
 
SECURITIES LENDING
 
The Company has entered into a securities lending agreement whereby certain
securities are loaned to third parties, primarily major brokerage firms. The
Company's policy requires a minimum of 102 percent of the fair value of the
loaned securities as collateral, calculated on a daily basis in the form of
either cash or securities. Collateral assets received and related liability due
to counterparties of $1.5 billion are included in the consolidated
 

                                       B-20
<PAGE>

                 THE NORTHWESTERN MUTUAL LIFE INSURANCE COMPANY
 
THE NORTHWESTERN MUTUAL LIFE INSURANCE COMPANY
 
NOTES TO CONSOLIDATED STATUTORY FINANCIAL STATEMENTS
 
DECEMBER 31, 1998, 1997 AND 1996
 
statements of financial position for each of the periods ended at December 31,
1998 and 1997, and approximate the statement value of securities loaned at those
dates.
 
INVESTMENT IN MGIC
 
The Company owns 11.0% (11.9 million shares) of the outstanding common stock of
MGIC Investment Corporation ("MGIC"). This investment is accounted for using the
equity method. At December 31, 1998 and 1997, the fair value of the Company's
investment in MGIC exceeded the statement value of $180 million and $273
million, respectively, by $296 million and $768 million, respectively.
 
In July 1995, the Company entered into a forward contract with a brokerage firm
to deliver 8.9 million to 10.7 million shares of MGIC (or cash in an amount
equal to the market value of the MGIC shares at contract maturity) in August,
1998, in exchange for a fixed cash payment of $247 million ($24 per share). The
Company's objective in entering into the forward contract was to hedge against
depreciation in the value of its MGIC holdings during the contract period below
the initial spot price of $24, while partially participating in appreciation, if
any, during the forward contract's duration. In August 1998, the Company
delivered 8.9 million shares to settle the forward contract. In conjunction with
the settlement, the Company recorded a $114 million realized gain.
 
DERIVATIVE FINANCIAL INSTRUMENTS
 
In the normal course of business, the Company enters into transactions to reduce
its exposure to fluctuations in interest rates, foreign currency exchange rates
and market volatility. These hedging strategies include the use of forwards,
futures, options and swaps.
 
The Company held the following positions for hedging purposes at December 31,
1998 and 1997:

<TABLE>
<CAPTION>
DERIVATIVE FINANCIAL INSTRUMENT                           NOTIONAL AMOUNTS                          RISKS REDUCED
- ---------------------------------------------  ---------------------------------------  ---------------------------------------
                                                            (IN MILLIONS)               
                                                  DECEMBER 31,                          
                                                      1998          DECEMBER 31, 1997   
                                               ------------------   ------------------  
<S>                                            <C>                  <C>              <C>
Foreign Currency Forward                                                                Currency exposure on foreign-denominated
 Contracts...................................         $601                 $564         investments.                           
Common Stock Futures.........................          657                  327         Stock market price fluctuation.        
Bond Futures.................................          379                   95         Bond market price fluctuation.         
Options to acquire Interest Rate Swaps.......          419                  530         Interest rates payable on certain annuity
                                                                                        and insurance contracts.                 
Foreign Currency and Interest Rate Swaps.....           94                  209         Interest rates on variable rate notes and
                                                                                        currency exposure on foreign-denominated
                                                                                        bonds.
</TABLE>
 
The notional or contractual amounts of derivative financial instruments are used
to denominate these types of transactions and do not represent the amounts
exchanged between the parties.
 
In addition to the use of derivatives for hedging purposes, equity swaps were
held for investment purposes during 1997 and 1998. The notional amount of equity
swaps outstanding at December 31, 1998 and 1997 was $188 million and $143
million, respectively.
 
Foreign currency forwards, foreign currency swaps, stock futures and equity
swaps are reported at fair value. Resulting gains and losses on these contracts
are unrealized until expiration of the contract. There is no statement


                                       B-21
<PAGE>

                 THE NORTHWESTERN MUTUAL LIFE INSURANCE COMPANY
 
THE NORTHWESTERN MUTUAL LIFE INSURANCE COMPANY
 
NOTES TO CONSOLIDATED STATUTORY FINANCIAL STATEMENTS
 
DECEMBER 31, 1998, 1997 AND 1996
 
value reported for interest rate swaps, bond futures and options to acquire
interest rate swaps prior to the settlement of the contract, at which time
realized gains and losses are deferred to IMR. Changes in the value of
derivative instruments are expected to offset gains and losses on the hedged
investments. During 1998, net realized and unrealized gains on investments were
partially offset by net realized losses of $104 million and net unrealized
losses of $58 million on derivative instruments. The effect of derivative
instruments in 1997 and 1996 was not material to the Company's results of
operations.
 
3. RESERVES FOR POLICY BENEFITS
 
Life insurance reserves on substantially all policies issued since 1978 are
based on the Commissioner's Reserve Valuation Method with interest rates ranging
from 3 1/2% to 5 1/2%. Other life policy reserves are primarily based on the net
level premium method employing various mortality tables at interest rates
ranging from 2% to 4 1/2%.
 
Deferred annuity reserves on contracts issued since 1985 are valued primarily
using the Commissioner's Annuity Reserve Valuation Method with interest rates
ranging from 3 1/2% to 6 1/4%. Other deferred annuity reserves are based on
contract value. Immediate annuity reserves are based on present values of
expected benefit payments at interest rates ranging from 3 1/2% to 7 1/2%.
 
Active life reserves for disability income ("DI") policies issued since 1987 are
primarily based on the two-year preliminary term method using a 4% interest rate
and the 1985 Commissioner's Individual Disability Table A ("CIDA") for
morbidity. Active life reserves for prior DI policies are based on the net level
premium method, a 3% to 4% interest rate and the 1964 Commissioner's Disability
Table for morbidity. Disabled life reserves for DI policies are based on the
present values of expected benefit payments primarily using the 1985 CIDA
(modified for Company experience in the first two years of disability) with
interest rates ranging from 3% to 5 1/2%.
 
Use of these actuarial tables and methods involves estimation of future
mortality and morbidity based on past experience. Actual future experience could
differ from these estimates.
 
4. EMPLOYEE AND AGENT BENEFIT PLANS
 
The Company sponsors noncontributory defined benefit retirement plans for all
eligible employees and agents. The expense associated with these plans is
generally recorded by the Company in the period contributions to the plans are
funded. As of January 1, 1998, the most recent actuarial valuation date
available, the qualified defined benefit plans were fully funded. The Company
recorded a liability of $98 million and $87 million for nonqualified defined
benefit plans at December 31, 1998 and 1997, respectively. In addition, the
Company has a contributory 401(k) plan for eligible employees and a
noncontributory defined contribution plan for all full-time agents. The
Company's contributions are expensed in the period contributions are made to the
plans. The Company recorded $29 million, $27 million and $25 million of total
expense related to its defined benefit and defined contribution plans for the
years ended December 31, 1998, 1997 and 1996, respectively. The defined benefit
and defined contribution plans' assets of $1.9 billion and $1.7 billion at
December 31, 1998 and 1997, respectively, were primarily invested in the
separate accounts of the Company.
 
In addition to pension and retirement benefits, the Company provides certain
health care and life insurance benefits ("postretirement benefits") for retired
employees. Substantially all employees may become eligible for these benefits if
they reach retirement age while working for the Company. Postretirement benefit
costs for the years ended December 31, 1998, 1997 and 1996 were a net expense
(benefit) of $1.8 million, ($1.3) million and
 

                                       B-22
<PAGE>

                 THE NORTHWESTERN MUTUAL LIFE INSURANCE COMPANY
 
THE NORTHWESTERN MUTUAL LIFE INSURANCE COMPANY
 
NOTES TO CONSOLIDATED STATUTORY FINANCIAL STATEMENTS
 
DECEMBER 31, 1998, 1997 AND 1996
 
($12.0) million, respectively. Net benefits were primarily a result of favorable
differences between actuarial assumptions and actual experience.
 
<TABLE>
<CAPTION>
                                    DECEMBER 31,          DECEMBER 31,
                                        1998                  1997
                                --------------------  --------------------
<S>                             <C>                   <C>
Unfunded postretirement
 benefit obligation for
 retirees and other fully
 eligible employees (Accrued
 in statement of financial
 position)....................  $35 million           $34 million
Estimated postretirement
 benefit obligation for active
 non-vested employees (Not
 accrued until employee
 vests).......................  $56 million           $50 million
Discount rate.................  7%                    7%
Health care cost trend rate...  10% to an ultimate    10% to an ultimate
                                5%, declining 1% for  5%, declining 1% for
                                5 years               5 years
</TABLE>
 
If the health care cost trend rate assumptions were increased by 1%, the accrued
postretirement benefit obligation as of December 31, 1998 and 1997 would have
been increased by $5 million and $4 million, respectively.
 
At December 31, 1998 and 1997, the recorded postretirement benefit obligation
was reduced by $23 million and $20 million, respectively, for assets funded for
postretirement health care benefits.
 
5. REINSURANCE
 
In the normal course of business, the Company seeks to limit its exposure to
loss on any single insured and to recover a portion of benefits paid by ceding
to reinsurers under excess coverage and coinsurance contracts. The Company
retains a maximum of $25 million of coverage per individual life and $35 million
maximum of coverage per joint life. The Company has an excess reinsurance
contract for disability income policies with retention limits varying based upon
on coverage type.
 
The amounts shown in the accompanying consolidated financial statements are net
of reinsurance. Policy benefit reserves at December 31, 1998 and 1997 were
reported net of ceded reserves of $518 million and $435 million, respectively.
The effect of reinsurance on premiums and benefits for the years ended December
31, 1998, 1997 and 1996 was as follows:
 
<TABLE>
<CAPTION>
                                                     1998      1997      1996
                                                    -------   -------   -------
                                                           (IN MILLIONS)
<S>                                                 <C>       <C>       <C>
Direct premiums...................................  $8,426    $7,647    $7,064
Premiums ceded....................................    (405)     (353)     (397)
                                                    -------   -------   -------
Net premium revenue...............................  $8,021    $7,294    $6,667
                                                    -------   -------   -------
                                                    -------   -------   -------
Benefits to policyowners and beneficiaries........  $8,869    $8,057    $7,348
Benefits ceded....................................    (182)     (136)     (147)
                                                    -------   -------   -------
Net benefits to policyowners and beneficiaries....  $8,687    $7,921    $7,201
                                                    -------   -------   -------
                                                    -------   -------   -------
</TABLE>


                                       B-23
<PAGE>

                 THE NORTHWESTERN MUTUAL LIFE INSURANCE COMPANY
 
THE NORTHWESTERN MUTUAL LIFE INSURANCE COMPANY
 
NOTES TO CONSOLIDATED STATUTORY FINANCIAL STATEMENTS
 
DECEMBER 31, 1998, 1997 AND 1996
 
In addition, the Company received $121 million, $115 million and $93 million for
the years ended December 31, 1998, 1997 and 1996, respectively, from reinsurers
representing allowances for reimbursement of commissions and other expenses.
These amounts are included in other income in the consolidated statement of
operations.
 
Reinsurance contracts do not relieve the Company from its obligations to
policyowners. Failure of reinsurers to honor their obligations could result in
losses to the Company; consequently, allowances are established for amounts
deemed uncollectible. The Company evaluates the financial condition of its
reinsurers and monitors concentrations of credit risk arising from similar
geographic regions, activities or economic characteristics of the reinsurers to
minimize its exposure to significant losses from reinsurer insolvencies.
 
6. INCOME TAXES
 
Provisions for income taxes are based on current income tax payable without
recognition of deferred taxes. The Company files a consolidated life-nonlife
federal income tax return. Federal income tax returns for years through 1988 are
closed as to further assessment of tax. Adequate provision has been made in the
financial statements for any additional taxes which may become due with respect
to the open years.
 
The Company's effective tax rate on gains from operations before taxes for the
years ended December 31, 1998, 1997 and 1996 was 48%, 56%, and 67% respectively.
The Company's effective tax rate exceeds the federal corporate rate of 35%
primarily because, (1) the Company pays a tax that is assessed only on the
surplus of mutual life insurance companies ("equity tax"), and (2) the Company
must capitalize and amortize (as opposed to immediately deducting) an amount
deemed to represent the cost of acquiring new business ("DAC tax").
 
7. ACQUISITION OF FRANK RUSSELL COMPANY
 
Pursuant to an Agreement and Plan of Merger, dated as of August 10, 1998, the
Company acquired Frank Russell Company effective January 1, 1999 for a purchase
price of approximately $950 million. Frank Russell is a leading investment
management and consulting firm, providing investment advice, analytical tools
and investment vehicles to institutional and individual investors in more than
30 countries.
 
In connection with its acquisition of Frank Russell Company, the Company will be
required in 1999 to charge-off directly from surplus approximately $341 million,
which represents the amount of acquisition goodwill less 10% of the Company's
surplus at December 31, 1998. In addition, the Company will request permission
from the OCI to charge-off the remaining $474 million of acquisition goodwill in
1999 and currently intends to do so.
 
In connection with the acquisition, the Company has unconditionally guaranteed
certain debt obligations of Frank Russell Company, including $350 million of
senior notes and up to $150 million of other credit facilities.
 
8. CONTINGENCIES
 
The Company has guaranteed certain obligations of its affiliates. These
guarantees totaled approximately $133 million at December 31, 1998 and are
generally supported by the underlying net asset values of the affiliates.
 
In addition, the Company routinely makes commitments to fund mortgage loans or
other investments in the normal course of business. These commitments aggregated
to $2.1 billion at December 31, 1998 and were extended at market interest rates
and terms.
 
The Company is engaged in various legal actions in the normal course of its
investment and insurance operations. In the opinion of management, any losses
resulting from such actions would not have a material effect on the Company's
financial position.
 

                                       B-24

<PAGE>

                            [LETTERHEAD]
 
REPORT OF INDEPENDENT ACCOUNTANTS
 
To the Board of Trustees and Policyowners of
 The Northwestern Mutual Life Insurance Company
 
We have audited the accompanying consolidated statement of financial position of
The Northwestern Mutual Life Insurance Company and its subsidiary as of December
31, 1998 and 1997, and the related consolidated statements of operations, of
changes in surplus and of cash flows for each of the three years in the period
ended December 31, 1998. These consolidated financial statements are the
responsibility of the Company's management. Our responsibility is to express an
opinion on these consolidated financial statements based on our audits.
 
We conducted our audits in accordance with generally accepted auditing
standards. Those standards require that we plan and perform the audit to obtain
reasonable assurance about whether the financial statements are free of material
misstatement. An audit includes examining, on a test basis, evidence supporting
the amounts and disclosures in the financial statements. An audit also includes
assessing the accounting principles used and significant estimates made by
management, as well as evaluating the overall financial statement presentation.
We believe that our audits provide a reasonable basis for our opinion.
 
As described in Note 1, these consolidated financial statements were prepared in
conformity with accounting practices prescribed or permitted by the Office of
the Commissioner of Insurance of the State of Wisconsin (statutory basis of
accounting), which practices differ from generally accepted accounting
principles. Accordingly, the consolidated financial statements are not intended
to represent a presentation in accordance with generally accepted accounting
principles. The effects on the consolidated financial statements of the
variances between the statutory basis of accounting and generally accepted
accounting principles, although not reasonably determinable, are presumed to be
material.
 
In our opinion, the consolidated financial statements audited by us (1) do not
present fairly in conformity with generally accepted accounting principles, the
financial position of The Northwestern Mutual Life Insurance Company and its
subsidiary at December 31, 1998 and 1997, or the results of their operations or
their cash flows for each of the three years in the period ended December 31,
1998 because of the effects of the variances between the statutory basis of
accounting and generally accepted accounting principles referred to in the
preceding paragraph and (2) do present fairly, in all material respects, the
financial position of The Northwestern Mutual Life Insurance Company and its
subsidiary at December 31, 1998 and 1997 and the results of their operations and
their cash flows for each of the three years in the period ended December 31,
1998, on the basis of accounting described in Note 1.
 
                    [SIGNATURE]
 
January 25, 1999


                                       B-25

<PAGE>

                             TABLE OF CONTENTS

<TABLE>
<CAPTION>
                                                                          PAGE
                                                                          ----
<S>                                                                       <C>
DISTRIBUTION OF THE CONTRACTS. . . . . . . . . . . . . . . . . . . . . . . B-2

DETERMINATION OF ANNUITY PAYMENTS. . . . . . . . . . . . . . . . . . . . . B-2
     Amount of Annuity Payments. . . . . . . . . . . . . . . . . . . . . . B-2
     Annuity Unit Value. . . . . . . . . . . . . . . . . . . . . . . . . . B-3
     Illustrations of Variable Annuity Payments. . . . . . . . . . . . . . B-3

VALUATION OF ASSETS OF THE ACCOUNT . . . . . . . . . . . . . . . . . . . . B-4

TRANSFERABILITY RESTRICTIONS . . . . . . . . . . . . . . . . . . . . . . . B-4

EXPERTS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-4

FINANCIAL STATEMENTS OF THE ACCOUNT. . . . . . . . . . . . . . . . . . . . B-5
(for the two years ended December 31, 1998)

REPORT OF INDEPENDENT ACCOUNTANTS . . . . . . . . . . . . . . . . . . . . B-11
(for the two years ended December 31, 1998)

FINANCIAL STATEMENTS OF NORTHWESTERN MUTUAL LIFE. . . . . . . . . . . . . B-12
(for the three years ended December 31, 1998)

REPORT OF INDEPENDENT ACCOUNTANTS . . . . . . . . . . . . . . . . . . . . B-25
(for the three years ended December 31, 1998)
</TABLE>

                                         B-26


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