<PAGE>
SEI INSTITUTIONAL MANAGED TRUST
TAX-MANAGED LARGE CAP FUND
SUPPLEMENT DATED MARCH 21, 2000 TO THE
CLASS A PROSPECTUSES DATED JANUARY 31, 2000
THIS SUPPLEMENT PROVIDES NEW AND ADDITIONAL INFORMATION BEYOND THAT CONTAINED IN
THE CLASS A PROSPECTUS, AND SHOULD BE READ IN CONJUNCTION WITH SUCH PROSPECTUS.
The Board of Trustees of SEI Institutional Managed Trust (the "Trust"),
including all of the Trustees who are not "interested persons" of the Trust,
have appointed Provident Investment Counsel, Inc. ("PIC"), as an additional
Sub-Adviser to the Trust's Tax-Managed Large Cap Fund (the "Fund"). PIC was
approved as a Sub-Adviser at the Quarterly Meeting of the Board of Trustees held
on March 20, 2000, and its appointment does not require Shareholder approval.
This procedure for adding or replacing Sub-Advisers was approved by the
Tax-Managed Large Cap Fund's sole initial shareholder on March 4, 1998, and was
authorized by an exemptive order issued to the Trust by the Securities and
Exchange Commission on April 29, 1996.
In evaluating PIC, the Trustees received written and oral information from both
SEI Investments Management Corporation ("SIMC") and PIC. SIMC recommended the
selection of PIC and reviewed the considerations and search process that led to
its recommendation. The Trustees also met with representatives of PIC and
considered information about portfolio managers, investment philosophy,
strategies and process, as well as other factors. In appointing PIC, the
Trustees carefully evaluated: (1) the nature and quality of the services
expected to be rendered to the Fund by PIC; (2) the distinct investment
objective and policies of the Fund; (3) the history, reputation, qualification
and background of PIC's personnel and its financial condition; (4) its
performance track record as manager of SEI Institutional Managed Trust's Large
Cap Growth Fund; and (5) other factors deemed relevant. The Trustees also
reviewed the fees to be paid to PIC, including any benefits to be received by
PIC or its affiliates in connection with soft dollar arrangements.
Under the Investment Sub-Advisory Agreement ("Sub-Advisory Agreement") between
SIMC (the "Adviser") and PIC relating to the Fund, PIC makes investment
decisions for the assets of the Fund allocated to it by SIMC, and continuously
reviews, supervises and administers the Fund's investment program with respect
to these assets. PIC is independent of SIMC and discharges its responsibilities
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 Sub-Advisers. Specifically,
the duties to be performed, standard of care and termination provisions of the
Agreement are similar to the other Agreements. The Sub-Advisory Agreement will
remain in effect until March 2002 (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 PIC as Sub-Adviser to the Fund, the
"Sub-Advisers" Section on page 21 of the Class A Prospectus is amended by
inserting the following disclosure relating to PIC:
PROVIDENT INVESTMENT COUNSEL, INC.: George E. Handtmann III and Jeffery J.
Miller of Provident Investment Counsel, Inc.("PIC"), serve as portfolio managers
of a portion of the assets of the Tax-Managed Large Cap Fund. Mr. Handtmann has
been with PIC since 1982, and Mr. Miller has been with PIC since 1972.
Listed below are the names and principal occupations of the principal executive
officers and directors of PIC. The principal business address of the principal
executive officers and directors, as it relates to their positions at PIC, is
300 North Lake Avenue, Pasadena, CA 91101.
<TABLE>
<CAPTION>
- --------------------------------------------------------------------------------------------------
NAME TITLE
<S> <C>
- --------------------------------------------------------------------------------------------------
Robert Marvin Kommerstad President/Chairman
- --------------------------------------------------------------------------------------------------
Jeffery John Miller Managing Director
- --------------------------------------------------------------------------------------------------
Thomas John Condon Managing Director
- --------------------------------------------------------------------------------------------------
Larry Dee Tashjian Executive Managing Director
- --------------------------------------------------------------------------------------------------
George Edward Handtmann III Executive Managing Director
- --------------------------------------------------------------------------------------------------
Senior Vice President and Chief Operations
Thad Michael Brown Officer
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Lauro Fernando Guerra Managing Director
- --------------------------------------------------------------------------------------------------
</TABLE>
The Adviser will pay PIC a fee based on a percentage of the average monthly
market value of the assets of the Fund assigned to PIC.
--------------------------
The Prospectus is hereby amended to reflect these changes.
PLEASE RETAIN THIS SUPPLEMENT FOR FUTURE REFERENCE
<PAGE>
SEI INSTITUTIONAL MANAGED TRUST
CORE FIXED INCOME FUND
SUPPLEMENT DATED MARCH 21, 2000 TO THE
PROSPECTUS DATED JANUARY 31, 2000
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 Managed Trust (the "Trust"),
including all of the Trustees who are not "interested persons" of the Trust,
have appointed Robert W. Baird & Co., Incorporated ("Baird"), as a Sub-Adviser
to the Trust's Core Fixed Income Fund (the "Fund"). Baird was approved as a
Sub-Adviser at the Quarterly Meeting of the Board of Trustees held on March 20,
2000, and its appointment does not require Shareholder approval. This procedure
for adding or replacing Sub-Advisers was approved by the Trust's sole initial
shareholder on November 13, 1995, and was authorized by an exemptive order
issued to the Trust by the Securities and Exchange Commission on April 29, 1996.
In evaluating Baird, the Trustees received written and oral information from SEI
Investments Management Corporation ("SIMC") and Baird. SIMC recommended the
selection of Baird and reviewed the considerations and the search process that
led to its recommendation. The Trustees also met with representatives of Baird
and considered information about portfolio managers, investment philosophy,
strategies and process, as well as its performance track record, among other
factors. In appointing Baird, the Trustees carefully evaluated: (1) the nature
and quality of the services expected to be rendered to the Fund by Baird; (2)
the distinct investment process of Baird; (3) the history, reputation,
qualification and background of Baird's personnel and its financial condition;
(4) its performance record; and (5) other factors deemed relevant. The Trustees
also reviewed the fees to be paid to Baird, including any benefits to be
received by Baird or its affiliates in connection with soft dollar arrangements.
Under the Investment Sub-Advisory Agreement ("Sub-Advisory Agreement") between
SIMC (the "Adviser") and Baird relating to the Fund, Baird makes investment
decisions for the assets of the Fund allocated to Baird by SIMC, and
continuously reviews, supervises and administers the Fund's investment program
with respect to these assets. Baird is independent of SIMC and discharges its
responsibilities subject to the supervision of SIMC and the Trustees of the
Trust and in a manner consistent with the Fund's investment objectives, policies
and limitations. The Sub-Advisory Agreement is substantially similar to those in
existence between the Adviser and the Trust's other sub-advisers. Specifically,
the duties to be performed under such 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 March 2002
(unless earlier terminated), and will have to be approved annually thereafter by
a majority of the Trust's 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 Baird as Sub-Adviser to the Fund, the
"Sub-Advisers" Section on page 7 of the Prospectus is amended by inserting the
following disclosure relating to Baird:
ROBERT W. BAIRD & CO., INCORPORATED
Robert W. Baird & Co., Incorporated ("Baird"), through its Baird Advisors
division, acts as a Sub-Adviser for a portion of the assets of the Core Fixed
Income Fund. Baird is a registered investment adviser. Baird currently has
approximately $6.4 billion in assets under management. The principal business
address of Baird is 777 E. Wisconsin Avenue, Milwaukee, Wisconsin 53202.
Charles B. Groeschell of Baird serves as portfolio manager of the portion of the
Fund's assets managed by Baird. Prior to joining Baird in March 2000, Mr.
Groeschell was a Senior Vice President and portfolio manager at Firstar
Investment Management & Research Company, LLC. Mr. Groeschell has over 17 years
of investment experience.
<PAGE>
Listed below are the names and principal occupations of the principal executive
officer and each of the directors of Baird. The principal business address of
the principal executive officer and each of the directors, as it relates to
their position at Baird, is 777 E. Wisconsin Avenue, Milwaukee, Wisconsin 53202.
<TABLE>
<CAPTION>
- --------------------------------------------------------------------------------------------------
NAME TITLE
<S> <C>
- --------------------------------------------------------------------------------------------------
George Frederick Kasten, Jr. Chief Executive Officer and Chairman
- --------------------------------------------------------------------------------------------------
Paul Edward Purcell President and Chief Operating Officer
- --------------------------------------------------------------------------------------------------
Glen Fredrick Hackmann Managing Director, Secretary, General Counsel
- --------------------------------------------------------------------------------------------------
James Dick Bell Managing Director
- --------------------------------------------------------------------------------------------------
Paul John Carbone Managing Director
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Bryce Patrick Edwards Managing Director
- --------------------------------------------------------------------------------------------------
Charles B. Groeschell Managing Director
- --------------------------------------------------------------------------------------------------
Keith Anthony Kolb Managing Director
- --------------------------------------------------------------------------------------------------
Patrick Steven Lawton Managing Director
- --------------------------------------------------------------------------------------------------
William Walter Mahler Managing Director
- --------------------------------------------------------------------------------------------------
Terrance Patrick Maxwell Managing Director
- --------------------------------------------------------------------------------------------------
John Robert Merrell Managing Director, Marketing Director
- --------------------------------------------------------------------------------------------------
Paul Stuart Shain Managing Director
- --------------------------------------------------------------------------------------------------
Russell Paul Schwei Managing Director, Chief Financial Officer
- --------------------------------------------------------------------------------------------------
Mary Ellen Stanek Managing Director
- --------------------------------------------------------------------------------------------------
Dominick Paul Zarcone Managing Director
- --------------------------------------------------------------------------------------------------
</TABLE>
The Adviser will pay Baird a fee based on a percentage of the average monthly
market value of the assets of the Fund assigned to Baird.
--------------------------
At the same meeting, the Board of Trustees of SEI Institutional Managed Trust
(the "Trust"), including all of the Trustees who are not "interested persons" of
the Trust, voted to terminate Firstar Investment Research & Management Company
("FIRMCO") as a Sub-Adviser to the Trust's Core Fixed Income Fund (the "Fund").
The Board determined to terminate FIRMCO because of the departure of FIRMCO's
portfolio management team to Baird. This termination does not require
Shareholder approval.
--------------------------
The prospectus is hereby amended to reflect these changes.
PLEASE RETAIN THIS SUPPLEMENT FOR FUTURE REFERENCE
