Background: Group A rotavirus genotypes G1, G2, G3 and G4 are the main etiological agents of infantile diarrhea. The G9 rotavirus has recently emerged as a fifth important genotype all over the world. Objective: To characterize the VP7 gene of group A rotaviruses from gastroenteritis patients admitted to the Gasthuisberg University Hospital, Leuven, Belgium, during 1999–2003. Study design: Rotavirus antigen was detected in stool specimens using an enzyme immunoassay. G-typing was performed by reverse transcriptase polymerase chain reaction (RT-PCR) amplification and sequencing of the complete VP7 gene. Results: The genotype distribution varied markedly over the four rotavirus years in Belgium. In the 1999–2000 rotavirus year, G1 was the predominating type (72%), and G9 was present in 5% of the rotavirus-positive patients. In the 2000–2001 and 2002–2003 years, G9 appeared as the dominating strain (45% and 53%, respectively). In the 2001–2002 year, between two G9 epidemic years, G1 was dominating (66%) but G9 was still present in 24%. All the G9 isolates were combined with P[8] and shared a high gene sequence similarity (