<PAGE>
MFS(R) MID CAP GROWTH FUND
Supplement dated January 1, 2000 as revised July 21, 2000
to the Current Prospectus
This Supplement describes the fund's class I shares, and it supplements certain
information in the fund's Prospectus dated January 1, 2000. The caption headings
used in this Supplement correspond with the caption headings used in the
Prospectus.
You may purchase class I shares only if you are an eligible institutional
investor, as described under the caption "Description of Share Classes" below.
1. RISK RETURN SUMMARY
Performance Table. The "Performance Table" is intended to indicate some of
the risks of investing in the fund by showing changes in the fund's
performance over time. The table is supplemented as follows:
Average Annual Total Returns as of December 31, 1998
1 Year 5 Years Life#
------ ------- -----
Class I shares 20.65% 15.52% 6.34%
Russell Midcap Growth Index+* 17.86% 17.34% 7.94%
Average mid-cap growth fund+ 12.39% 14.86% 5.55%
---------------------------------
# Fund performance figures are for the period from the commencement of the
fund's investment operations on December 1, 1993 through December 31,
1998. Index and Lipper average returns are from December 1, 1993.
+ Source: Lipper Analytical Services, Inc.
* The Russell Midcap Growth Index is a broad based, unmanaged index which
measures the performance of the smallest growth companies in the Russell
1000 Index. It is not possible to invest directly in an index.
The fund commenced investment operations on December 1, 1993 with the offering
of class A and class B shares, and subsequently offered class I shares on
January 2, 1997. Class I share performance includes the performance of the
fund's class A shares for periods prior to the offering of class I shares. This
blended class I share performance has been adjusted to take into account the
fact that class I shares have no initial sales charge (load). This blended
performance has not been adjusted to take into account differences in class
specific operating expenses. Because operating expenses of class I shares are
lower than those of class A shares, this blended class I share performance is
lower than the performance of class I shares would have been had class I shares
been offered for the entire period.
2. EXPENSE SUMMARY
Expense Table. The "Expense Table" describes the fees and expenses that you
may pay when you buy, redeem and hold shares of the fund. The table is
supplemented as follows:
Annual Fund Operating Expenses (expenses that are deducted from fund
assets):
Management Fees................................. 0.75%
Distribution and Service (12b-1) Fees........... None
Other Expenses.................................. 0.32%
-----
Total Annual Fund Operating Expenses(1)......... 1.07%
--------------------------
(1) The fund has an expense offset arrangement which 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 under "Other Expenses."
3. 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.
<PAGE>
These 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.
Although your actual costs may be higher or lower, under these assumptions your
costs would be:
Share Class Year 1 Year 3 Year 5 Year 10
----------- ------ ------ ------ -------
Class I shares $109 $340 $590 $1,306
4. DESCRIPTION OF SHARE CLASSES
The "Description of Share Classes" is supplemented as follows:
If you are an eligible institutional investor (as described below), you may
purchase class I shares at net asset value without an initial sales charge or
CDSC upon redemption. Class I shares do not have annual distribution and service
fees, and do not convert to any other class of shares of the fund.
The following eligible institutional investors may purchase class I shares:
o certain retirement plans established for the benefit of employees of
MFS and employees of MFS' affiliates;
o any fund distributed by MFD, if the fund seeks to achieve its
investment objective by investing primarily in shares of the fund and
other MFS funds:
o any retirement plan, endowment or foundation which:
has, at the time of purchase of class I shares, aggregate assets of at
least $100 million, and
invests at least $10 million in class I shares of the fund either
alone or in combination with investments in class I shares of other
MFS Funds (additional investments may be made in any amount).
MFD may accept purchases from smaller plans, endowments or foundations or in
smaller amounts if it believes, in its sole discretion, that such entity's
aggregate assets will equal or exceed $100 million, or that such entity will
make additional investments which will cause its total investment to equal or
exceed $10 million, within a reasonable period of time;
o bank trust departments or law firms acting as trustee or manager for
trust accounts which, on behalf of their clients (i) initially invest
at least $100,000 in class I shares of the fund or (ii) have, at the
time of purchase of class I shares, aggregate assets of at least $10
million invested in class I shares of the fund either alone or in
combination with investments in class I shares of other MFS Funds. MFD
may accept purchases that do not meet these dollar qualification
requirements if it believes, in its sole discretion, that these
requirements will be met within a reasonable period of time. Additional
investments may be made in any amount; and
o certain retirement plans offered, administered or sponsored by
insurance companies, provided that these plans and insurance companies
meet certain criteria established by MFD from time to time.
5. HOW TO PURCHASE, EXCHANGE AND REDEEM SHARES
The discussion of "How to Purchase, Exchange and Redeem Shares" is supplemented
as follows:
You may purchase, redeem and exchange class I shares only through your MFD
representative or by contacting MFSC (see the back cover of the Prospectus for
address and phone number). You may exchange your class I shares for class I
shares of another MFS Fund (if you are eligible to purchase them) and for
shares of the MFS Money Market Fund at net asset value.
<PAGE>
6. FINANCIAL HIGHLIGHTS
The "Financial Highlights" table is intended to help you understand the fund's
financial performance. It is supplemented as follows:
Financial Statements - Class I shares
<TABLE>
<CAPTION>
<S> <C> <C> <C>
Year Ended August 31 Period Ended
1999 1998 August 31, 1997*
---- ---- ----------------
Per share data (for a share outstanding throughout each period):
Net asset value - beginning of period $ 7.73 $ 9.44 $ 8.50
-------- -------- --------
Income from investment operations# -
Net investment loss $ (0.04) $ (0.08) $ (0.05)
Net realized and unrealized gain (loss) on investments
and foreign currency 5.04 (1.32) 0.99
--------- ---------- --------
Total from investment operations $ 5.00 $ (1.40) $ 0.94
-------- --------- --------
Less distributions declared to shareholders from net realized
gain on investments and foreign currency transactions $ (1.36) $ (0.31) $ --
--------- --------- ------
Net asset value - end of period $ 11.37 $ 7.73 $ 9.44
------- -------- --------
Total return 69.03% (15.23)% 11.06%++
Ratios (to average net assets)/Supplemental data:
Expenses## 1.07% 1.18% 1.03%+
Net investment loss (0.44)% (0.82)% (0.74)%+
Portfolio turnover 158% 168% 170%
Net assets at end of period (000 omitted) $1,841 $925 $1,384
</TABLE>
--------------------------
* For the period from the inception of class I, January 2, 1997 through
August 31, 1997.
+ Annualized.
++ Not annualized.
# Per share data are based on average shares outstanding.
## The fund has an expense offset arrangement which reduces the fund's
custodian fee based upon the amount of cash maintained by the fund with its
custodian and dividend disbursing agent. The fund's expenses are calculated
without reduction for this expense offset arrangement. The date of this
Supplement is January 1, 2000 as revised July 21, 2000.
