Certification Pursuant to 18 U.S.C. Section 1350,
                             As Adopted Pursuant to
                  Section 906 of the Sarbanes-Oxley Act of 2002


Name of Issuer: Vanguard Institutional Index Funds

     In connection with the Report on Form N-CSR of the above-named  issuer that
is accompanied by this certification,  the undersigned hereby certifies,  to his
knowledge, that:

1.   The Report fully complies with the  requirements  of Section 13(a) or 15(d)
     of the Securities Exchange Act of 1934; and

2.   The information  contained in the Report fairly  presents,  in all material
     respects, the financial condition and results of operations of the issuer.


Date:  August 16, 2004

                                                            /S/ JOHN J. BRENNAN
                                                    ----------------------------
                                                         CHIEF EXECUTIVE OFFICER










                Certification Pursuant to 18 U.S.C. Section 1350,
                             As Adopted Pursuant to
                  Section 906 of the Sarbanes-Oxley Act of 2002


Name of Issuer:  Vanguard Institutional Index Funds

     In connection with the Report on Form N-CSR of the above-named  issuer that
is accompanied by this certification,  the undersigned hereby certifies,  to his
knowledge, that:

1.   The Report fully complies with the  requirements  of Section 13(a) or 15(d)
     of the Securities Exchange Act of 1934; and

2.   The information  contained in the Report fairly  presents,  in all material
     respects, the financial condition and results of operations of the issuer.


Date: August 16, 2004


                                                        /S/ THOMAS J. HIGGINS
                                                       -------------------------
                                                                       TREASURER