<PAGE>
MFS(R) INSTITUTIONAL TRUST
MFS(R) INSTITUTIONAL MID CAP GROWTH FUND
Supplement dated December 15, 2000 to the Current Prospectus
Effective November 1, 2000, the Expense Summary section for the above referenced
funds (each a "fund") is hereby amended and restated as follows:
EXPENSE SUMMARY
Expense Table. The "Expense Table" describes expenses you may pay when you
hold shares of the fund.
Annual Fund Operating Expenses (expenses that are deducted from fund
assets):
Mid Cap Fund
Management Fees 0.60%
Other Expenses 0.15%
-----
Total Annual Fund Operating Expenses 0.75%
Fee Waiver/ Expense Reimbursement(1) (0.09)%
-------
Net Expenses(2) 0.66%
-----------------------------
(1) MFS has contractually agreed to bear the fund's "Other Expenses", after
giving effect to the expense offset arrangement described below, such
that "Other Expenses" do not exceed 0.05% annually. These contractual fee
arrangements will remain in effect until at least November 1, 2001,
absent an earlier modification approved by the board of trustees which
oversees the fund.
(2) The fund has an expense offset arrangement that reduces the fund's
custodian fee based upon the amount of cash maintained by the fund with
its custodian and dividend disbursing agent, and may enter into other
such arrangements and directed brokerage arrangements (which would also
have the effect of reducing the fund's expenses). Any such fee reductions
are not reflected in the table. Had these fee reductions been taken into
account, "Net Expenses" would be lower for the fund, and would equal
0.65%.
Example of Expenses. The "Example of Expenses" table is intended to help you
compare the cost of investing in the fund with the cost of investing in other
mutual funds. The examples assume that:
o You invest $10,000 in the fund for the time periods indicated and you
redeem your shares at the end of the time periods;
o Your investment has a 5% return each year and dividends and other
distributions are reinvested; and
o The fund's operating expenses remain the same, except that the fund's
total operating expenses are assumed to be the fund's "Net Expenses"
for the first year, and the fund's "Total Annual Fund Operating
Expenses" for subsequent years (see the table above).
Series Year 1 Year 3 Year 5 Year 10
Mid Cap Fund $67 $231 $408 $922
The date of this Supplement is December 15, 2000.
