ROBECO INVESTMENT FUNDS

                     INSTITUTIONAL CLASS AND INVESTOR CLASS

                   ROBECO BOSTON PARTNERS Large Cap Value Fund
                    ROBECO BOSTON PARTNERS Mid Cap Value Fund
                 ROBECO BOSTON PARTNERS Small Cap Value Fund II
                    ROBECO BOSTON PARTNERS All-Cap Value Fund
                  ROBECO BOSTON PARTNERS Long/Short Equity Fund

                         Supplement dated August 8, 2005
                     to Prospectuses dated December 31, 2004

THIS SUPPLEMENT CONTAINS NEW AND ADDITIONAL INFORMATION BEYOND THAT CONTAINED IN
THE PROSPECTUS AND SHOULD BE READ IN CONJUNCTION WITH THE PROSPECTUS.

         INSERT THE FOLLOWING AS THE SECOND PARAGRAPH UNDER THE SUB-PARAGRAPH OF
THE PROSPECTUS  ENTITLED "ROBECO BOSTON PARTNERS LARGE CAP VALUE FUND" UNDER THE
CAPTION "PORTFOLIO  MANAGERS" IN THE SECTION ENTITLED  "MANAGEMENT OF THE FUNDS"
ON PAGE 36 OF THE INVESTOR CLASS PROSPECTUS AND ON PAGE 37 OF THE  INSTITUTIONAL
CLASS PROSPECTUS:

         Effective  December  31,  2005,  Wayne S.  Sharp  will be  retiring  as
portfolio  manager of the Robeco Boston Partners Large Cap Fund. In anticipation
of this change,  effective  August 8, 2005,  David J. Pyle has been named as Ms.
Sharp's  successor.  Ms. Sharp will  continue to manage the Fund in  conjunction
with  Messrs.  Donovan  and Pyle  until her  retirement.  Mr.  Pyle is an equity
portfolio manager for Robeco Boston Partners' Large Cap Value product, and prior
to that  position,  he was a research  analyst  specializing  in the  utilities,
insurance,  leisure & lodging,  packaging,  publishing, and computer equipment &
services  sectors of the equity market.  Prior to joining the Adviser in January
2000,  Mr. Pyle was employed by State Street  Research as an equity  analyst and
associated  portfolio manager working for the Value Group. Mr. Pyle is a CFA and
member  of the  Boston  Security  Analysts  Society.  Mr.  Pyle  has 10 years of
experience in the investment industry.

         INSERT THE FOLLOWING AS THE SECOND PARAGRAPH UNDER THE SUB-PARAGRAPH OF
THE PROSPECTUS  ENTITLED  "ROBECO BOSTON PARTNERS  ALL-CAP VALUE FUND" UNDER THE
CAPTION "PORTFOLIO  MANAGERS" IN THE SECTION ENTITLED  "MANAGEMENT OF THE FUNDS"
ON PAGE 37 OF THE INVESTOR CLASS PROSPECTUS AND ON PAGE 38 OF THE  INSTITUTIONAL
CLASS PROSPECTUS:

         Effective  August 8, 2005,  Duilio R. Ramallo will become  co-portfolio
manager of the Robeco Boston Partners  All-Cap Value Fund,  replacing  Steven L.
Pollack,  the secondary  manager of the Fund.  Harry  Rosenbluth  remains as the
other  co-portfolio  manager  on the  Fund.  However,  Mr.  Rosenbluth  plans on
retiring from the day to day  management of the All-Cap Value Fund at the end of
2006. Mr. Ramallo is an equity portfolio  manager for Boston  Partners'  Premium
Equity product and prior to this position was an assistant portfolio manager for
the small cap value  products.  Prior to his  portfolio  management  roles,  Mr.
Ramallo was a research analyst for the Adviser.  Prior to joining the Adviser in
December 1995, Mr. Ramallo spent three years with Deloitte & Touche LLP. He is a
member of the CFA  Institute and the Los Angeles  Society of Financial  Analysts
and has a total of 10 years of investment experience.

               PLEASE RETAIN THIS SUPPLEMENT FOR FUTURE REFERENCE.