In 1999, Sereni returned to Sampdoria in Serie B, made 75 (out of 76) Serie B appearances. In 2001, UEFA Cup competitor Ipswich Town signed him for €7.5million, the highest transfer fee paid by the club. He failed to avoid relegation with Ipswich and was loaned to Brescia in 2002.
In 2003, he transferred to Lazio, to compete for number one goalkeeper at the club with Angelo Peruzzi. In 2004, he started for the club in both legs of the Coppa Italia final against Juventus and played the matches in 2005 Intertoto Cup, when Lazio went out to Olympique de Marseille in the semi-finals.
In January 2006, he was loaned out to Treviso, with Samir Handanović on loan to Lazio. He returned to Lazio for the 2006-07 campaign, but did not achieve a single match, being excluded by the roster for the whole season. On June 2007 he signed for Torino in a free transfer to replace Christian Abbiati.
He was internationally selected at the age of 16 for the Italian national under-17 team, and played for the Italian national under-23 team at the 1997 Mediterranean Games, where Italy were champions.