<PAGE>
May 16, 2000
(ON JOHN NUVEEN & CO. INCORPORATED LETTERHEAD)
SECURITIES AND EXCHANGE COMMISSION
450 FIFTH STREET, N.W.
WASHINGTON, D.C. 20549
Attention: Filing Desk
Stop 1-4
RE: Nuveen Unit Trusts, Series 91
File No. 333-36520
Dear Sir or Madam:
On behalf of John Nuveen & Co. Incorporated, in accordance with the
provisions of Rule 497(j) of Regulation C under the Securities Act of 1933
(the "Securities Act"), this letter serves to certify that the most recent
amendment to the Registration Statement on Form S-6 (the "Registration
Statement") of the above-referenced Series does not differ from that which
would have been filed pursuant to Rule 497(b) of the Securities Act.
Amendment No. 2, which was the most recent amendment to the Registration
Statement, was filed electronically with the Commission on May 15, 2000.
JOHN NUVEEN & CO. INCORPORATED
By /s/ Benjamin T. Fulton
------------------------------------
Benjamin T. Fulton
Managing Director and Vice President
