The 1991 Campionati Internazionali di San Marino was a men's tennis tournament played on outdoor clay courts at the Centro Tennis Cassa di Risparmio di Fonte dell'Ovo in the City of San Marino in San Marino and was part of the World Series of the 1991 ATP Tour. It was the third edition of the tournament and was held from 29 July until 4 August 1991. First-seeded Guillermo Pérez Roldán won his second consecutive singles title at the event.[1]
See main article: 1991 Campionati Internazionali di San Marino – Singles. 
Guillermo Pérez Roldán defeated 
Frédéric Fontang 6–3, 6–1
See main article: 1991 Campionati Internazionali di San Marino – Doubles. 
Jordi Arrese / Carlos Costa defeated Christian Miniussi / Diego Pérez 6–3, 3–6, 6–3