He officially joined Perugia Calcio of the Serie A in July 2001, and in his debut Serie A season, Grosso managed an impressive 24 appearances with a single goal. By now he had been converted into a left wing back by coach Serse Cosmi, and in his second season in Perugia, Grosso maintained a starting position and made 30 league appearances with 4 goals. In his third season with Perugia, Grosso made just 12 appearances in the first 6 months of the 2003–04 season. To some surprise, Grosso transferred away from Perugia in January 2004, and was sold to Palermo, who, at the time, played in the Italian Serie B. In 2003, during his time with Perugia, Grosso earned his first Italy cap.