<PAGE>
SEI INSTITUTIONAL INVESTMENTS TRUST
INTERNATIONAL EQUITY FUND
SMALL CAP FUND
SUPPLEMENT DATED JUNE 29, 1998,
TO THE PROSPECTUS DATED SEPTEMBER 30, 1997
THIS SUPPLEMENT PROVIDES NEW AND ADDITIONAL INFORMATION BEYOND THAT CONTAINED IN
THE PROSPECTUS, AND SHOULD BE READ IN CONJUNCTION WITH SUCH PROSPECTUS.
The Board of Trustees of SEI Institutional Investments Trust (the "Trust"),
including all of the Trustees who are not "interested persons" of the Trust,
appointed Capital Guardian Trust Company ("Capital Guardian") as a Money Manager
to the Trust's International Equity Fund (the "Fund"). Capital Guardian was
approved as a Money Manager at the Quarterly Meeting of the Board of Trustees
held on June 10, 1998, and its appointment does not require Shareholder
approval. This procedure for adding money managers was approved by the Trust's
sole initial shareholder on June 14, 1996, and was authorized by an exemptive
order issued to the Trust by the Securities and Exchange Commission on April 29,
1996.
In evaluating Capital Guardian, the Trustees received written and oral
information from SEI Investments Management Corporation ("SIMC") and Capital
Guardian. SIMC recommended the selection of Capital Guardian and reviewed the
considerations and the search process that led to its recommendation. The
Trustees also met with representatives of Capital Guardian and considered
information about portfolio managers, investment philosophy, strategy and
process, as well as its performance track record, among other factors. In
appointing Capital Guardian, the Trustees carefully evaluated: (1) the nature
and quality of the services expected to be rendered to the Fund by Capital
Guardian; (2) the distinct investment objective and policies of the Fund; (3)
the history, reputation, qualification and background of Capital Guardian's
personnel and financial condition; (4) its performance track record; and (5)
other factors deemed relevant. The Trustees also reviewed the fees to be paid to
Capital Guardian, including any benefits to be received by Capital Guardian or
its affiliates in connection with soft dollar arrangements.
Under the Investment Sub-Advisory Agreement (the "Sub-Advisory Agreement")
between SIMC (the "Adviser") and Capital Guardian relating to the Fund, Capital
Guardian makes investment decisions for the assets of the Fund allocated to it
by SIMC, continuously reviews, supervises and administers the Fund's investment
program with respect to these assets. Capital Guardian is independent of SIMC
and discharges its responsibility subject to the supervision of SIMC and the
Trustees of the Trust and in a manner consistent with the Fund's investment
objective, policies and limitations. The Sub-Advisory Agreement is substantially
similar to those in existence between the Adviser and the Trust's other Money
Managers. Specifically, the duties to be performed under the Agreement are
similar, and the standard of care and termination provisions of the Agreement
are identical, to the other Agreements. The Sub-Advisory Agreement will remain
in effect until June 2000 (unless earlier terminated), and will have to be
approved annually thereafter by a majority of the Trustees, including a majority
of the Trustees who are not "interested persons" of the Trust (as defined in the
Investment Company Act of 1940).
In connection with the appointment of Capital Guardian as Money Manager to the
Fund, "The Money Managers" Section on page 16 of the Prospectus is amended by
inserting the following disclosure:
CAPITAL GUARDIAN TRUST COMPANY
Capital Guardian Trust Company ("Capital Guardian") acts as a Money Manager for
a portion of the assets of the International Equity Fund. Capital Guardian is a
California trust company founded in 1968, and is a wholly-owned subsidiary of
The Capital Group Companies, Inc. Capital Guardian has managed international
portfolios since 1978, and as of March 31, 1998, managed a total of over $77
billion, primarily for institutional clients. The principal business address of
Capital Guardian and The Capital Group Companies, Inc. is 333 South Hope Street,
Los Angeles, California 90071.
<PAGE>
Capital Guardian utilizes a multiple portfolio management system under which a
group of portfolio managers each will have investment discretion over a portion
of the assets of the Fund managed by Capital Guardian. Capital Guardian utilizes
a research driven, value-oriented investment philosophy.
------------------------------------------------------------
The description of Nicholas-Applegate in the "Money Managers" section of the
prospectus is hereby replaced with the following language:
NICHOLAS-APPLEGATE CAPITAL MANAGEMENT
Nicholas-Applegate Capital Management ("Nicholas-Applegate") serves as a Money
Manager for a portion of the assets of the Small Cap Fund. Nicholas-Applegate
has operated as an investment adviser which provides investment services to
numerous clients, including employee benefit plans, public retirement systems
and unions, university endowments, foundations, investment companies, other
institutional investors and individuals. As of June 30, 1997, Nicholas-Applegate
had discretionary management authority with respect to approximately $30.3
billion of assets. The principal business address of Nicholas-Applegate is 600
West Broadway, 29th Floor, San Diego, California 92101. Nicholas-Applegate,
pursuant to a partnership agreement, is controlled by its general partner,
Nicholas-Applegate Capital Management Holdings, L.P., a California limited
partnership controlled by a corporation controlled by Arthur E. Nicholas.
Nicholas-Applegate manages its portion of the Small Cap Fund's assets through
its systematic-driven management team under the general supervision of Mr.
Nicholas, founder and Chief Investment Officer of the firm. The U.S. Systematic
team is responsible for the day-to-day management of the Fund's assets. The lead
U.S. Systematic portfolio manager is John Kane, and he is assisted by five other
portfolio manager/ analysts for the Fund's U.S. Systematic assets. Mr. Kane has
been a fund manager and investment team leader since June 1994. Prior to joining
Nicholas-Applegate, he had 25 years of investment/economics experience with ARCO
Investment Management Company and General Electric Company.
PLEASE RETAIN THIS SUPPLEMENT FOR FUTURE REFERENCE.
2
