<PAGE>
SUPPLEMENT DATED DECEMBER 27, 1999
TO PROSPECTUS DATED MAY 1, 1999, AS AMENDED AND SUPPLEMENTED THROUGH
OCTOBER 12, 1999
OF
EQUITY GROWTH PORTFOLIO
FOCUS EQUITY PORTFOLIO
SMALL COMPANY GROWTH PORTFOLIO
VALUE EQUITY PORTFOLIO
TECHNOLOGY PORTFOLIO
PORTFOLIOS OF
MORGAN STANLEY DEAN WITTER INSTITUTIONAL FUND, INC.
P.O. BOX 2798
BOSTON, MASSACHUSETTS
02208-2798
---------------------
The Prospectus is hereby amended and supplemented to reflect that the
Technology Portfolio will not sell short. Accordingly, the third paragraph under
"RISK" on page 5 is hereby deleted and replaced with the following:
The risks of investing in the Portfolio may be intensified because the Portfolio
is non-diversified, which means that it may invest in securities of a limited
number of issuers. As a result, the performance of a particular investment or a
small group of investments may affect the Portfolio's performance more than if
the Portfolio were diversified.
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PLEASE RETAIN THIS SUPPLEMENT FOR FUTURE REFERENCE
<PAGE>
SUPPLEMENT DATED DECEMBER 27, 1999
TO STATEMENT OF ADDITIONAL INFORMATION DATED MAY 1, 1999,
AS AMENDED AND SUPPLEMENTED THROUGH OCTOBER 1, 1999
MORGAN STANLEY DEAN WITTER INSTITUTIONAL FUND, INC.
P.O. BOX 2798
BOSTON, MASSACHUSETTS
02208-2798
---------------------
The Statement of Additional Information is being supplemented to reflect
that the Technology Portfolio will not sell short or borrow money except as
stated below. Accordingly, the first and seventh non-fundamental limitations on
page 24 are hereby deleted and replaced with the following:
Each current Portfolio of the Fund will not:
(1) purchase on margin or sell short, except (i) that the Emerging Markets Debt,
Latin American, and Focus Equity Portfolios may from time to time sell
securities short without limitation but consistent with applicable legal
requirements as stated in its Prospectus; (ii) that each Portfolio, except
the Money Market and Municipal Money Market Portfolios, may enter into
option transactions and futures contracts as described in its Prospectus;
and (iii) as specified above in fundamental investment limitation number
(1) above;
(7) borrow money, except from banks for extraordinary or emergency purposes, and
then only in amounts up to 10% of the value of the Portfolio's total assets,
or purchase securities while borrowings exceed 5% of its total assets,
except that (i) the Emerging Markets Debt Portfolio may borrow in accordance
with fundamental investment limitation number (5) above; and (ii) the High
Yield Portfolio may borrow up to 33 1/2% of its total assets in the
aggregate, including reverse repurchase agreements; and
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The chart on page 4 is hereby deleted and replaced with the following:
<TABLE>
<CAPTION>
U.S. EQUITY PORTFOLIOS
SMALL U.S. U.S.
FOCUS COMPANY EQUITY EQUITY REAL VALUE
EQUITY GROWTH GROWTH MICROCAP TECHNOLOGY PLUS ESTATE EQUITY
--------- --------- --------- --------- ---------- --------- --------- ---------
<S> <C> <C> <C> <C> <C> <C> <C> <C>
FIXED INCOME SECURITIES:
Mortgage Related Securities....
--MBSs.........................
--CMOs.........................
--SMBSs........................
Repurchase Agreements.......... X X X X X X X X
Municipals.....................
Asset-Backeds..................
Loan Participations and
Assignments..................
Temporary Investments.......... X X X X X X X X
Zero Coupons, Pay-In-Kind
Securities or Deferred
Payment Securities........... X X X X X X X X
Floaters.......................
Inverse Floaters...............
</TABLE>
<PAGE>
<TABLE>
<CAPTION>
U.S. EQUITY PORTFOLIOS (CONTINUED)
SMALL U.S. U.S.
FOCUS COMPANY EQUITY EQUITY REAL VALUE
EQUITY GROWTH GROWTH MICROCAP TECHNOLOGY PLUS ESTATE EQUITY
--------- --------- --------- --------- ---------- --------- --------- ---------
<S> <C> <C> <C> <C> <C> <C> <C> <C>
FOREIGN INVESTMENT:
Foreign Equity Securities...... X X X X X X X X
Foreign Bonds.................. X X
Emerging Market Country
Securities................... X X
Russian Equity Securities......
Foreign Currency
Transactions................. X X X X X X X X
Brady Bonds....................
Investment Funds............... X X X X X X X X
OTHER SECURITIES AND INVESTMENT
TECHNIQUES:
Loans of Portfolio
Securities................... X X X X X X X X
Non-Publicly Traded Securities,
Private Placements and
Restricted Securities........ X X X X X X X X
When-Issued and Delayed
Delivery Securities.......... X X X X X X X X
Borrowing for Investment
Purposes..................... X
Temporary Borrowing............ X X X X X X X X
Reverse Repurchase
Agreements................... X X
Short Sales.................... X
Structured Investments......... X X X X X X X X
DERIVATIVE PRODUCTS:
Foreign Currency Forward
Contracts.................... X X X X X X X X
Futures Contracts.............. X X X X X X X X
Forward Contracts.............. X X X X X X X X
Option Transactional........... X X X X X X X X
Swaps.......................... X X X X X X X X
</TABLE>
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PLEASE RETAIN THIS SUPPLEMENT FOR FUTURE REFERENCE
