Small round-structured viruses (SRSV) are a group of RNA viruses that can cause gastroenteritis in persons of all ages. To determine the incidence of SRSV-associated gastroenteritis in The Netherlands and to study the genetic variability of outbreak strains, all outbreaks that were reported to the epidemiologists of the regional health services in 1996 were investigated using a standardized protocol. In 60 (87%) of the 69 reported outbreaks, SRSV could be detected, showing the etiologic significance of SRSV in outbreaks of gastroenteritis in The Netherlands. Of these outbreaks, 84% occurred in semiclosed communities, such as nursing homes (59%) and hospital wards (25%). Sequence analysis of the outbreak strains revealed that the majority of the strains from January to November 1996 formed a tight cluster within genogroup II SRSV. In November 1996, a shift toward genogroup I SRSV occurred, suggesting a change to a new predominant strain.