The 1991 Norstar Bank Hamlet Challenge Cup was a men's tennis tournament played on outdoor hard courts.

It was the 11th edition of the event known that year as the Norstar Bank Hamlet Challenge Cup, and was part of the World Series of the 1991 ATP Tour.

2, Australian Open and Wimbledon semifinalist, Stuttgart, Tokyo indoor and Queen's Club winner, Long Island defending champion Stefan Edberg, Australian Open runner-up, Philadelphia and Memphis champion Ivan Lendl, and Wimbledon semifinalist, Miami finalist David Wheaton.

Also present were Chicago titlist John McEnroe, Manchester winner Goran Ivanišević, Jonas Svensson, Alberto Mancini and Omar Camporese.

Second-seeded Ivan Lendl, who entered the draw on a wildcard, won the singles title and earned $32,400 first-prize money.