The 1991 Monte Carlo Open was a men's tennis tournament played on outdoor clay courts.

The men's singles field was headlined by Stefan Edberg and Boris Becker.

Other top seeds in the field were Guy Forget, Andre Agassi, and Goran Ivanišević.

Ninth-seeded Sergi Bruguera won the singles title.

[3] Sergi Bruguera defeated Boris Becker, 5–7, 6–4, 7–6(8–6), 7–6(7–4) Luke Jensen / Laurie Warder defeated Paul Haarhuis / Mark Koevermans, 5–7, 7–6, 6–4