Altobelli was born in Sonnino, Latina. Following spells at Latina (Serie C) and Brescia (Serie B), he was signed by Serie A club Internazionale in 1977, for whom he played 466 times, scoring 209 goals (128 in Serie A). He contributed heavily to his team's scudetto victory of 1980 (scoring 15 goals), and also helped Inter to win two Coppa Italia titles in 1978 and 1982, finishing as the tournament's top scorer in the 1982 edition, with nine goals. Altobelli was also the top scorer in the 1978–79 European Cup Winners' Cup, with seven goals, leading Inter to the quarter-finals of the tournament. After his lengthy period with Inter, he played one season with Juventus during the 1987–88 season, before ending his career with Brescia in Serie B once again, during the 1989–90 season.