The 1991 Pittsburgh Pirates season was the 110th in franchise history; the 105th in the National League. This was their 22nd season at Three Rivers Stadium. For the second consecutive season, the Pirates won the National League East Division Title with a record of 98–64. The Pirates finished the season with the best record in the league. They were defeated four games to three by the Atlanta Braves in the 1991 National League Championship Series. During the season, John Smiley won 20 games – the last to do so for the Pirates in the 20th century.