Rotavirus infections are a major cause of severe diarrhea in children younger than 2 years. In Belgium they cause many hospitalizations because of dehydration. A study of the laboratory diagnosis of rotavirus infections in 28.251 stool samples at a university teaching hospital in Belgium during a twenty-year period (1981-2002) showed a marked seasonality. The virus was most often diagnosed during the winter months: 54% of the rotavirus isolates were found in the first three months of the year, with 21% of the positive samples occurring in February. Recently, rotaviruses can be genotyped based on differences in the viral outer capsid protein VP7. Vaccines are currently being developed against the four most prevalent genotypes G1, G2, G3 and G4. During the last three epidemic seasons (1999-2002) in Belgium, G1 was the most prevalent genotype and accounted for 62% of the rotavirus isolates recovered. G2, G3 and G4 were also isolated, and other emerging types need to be carefully monitored too, since G9 (45%) was co-dominant with G1 (42%) in the 2000-2001 rotavirus season in Belgium. The future development of an efficient rotavirus vaccine will need to take the diversity of the rotavirus genotypes into account.