AbstractAn outbreak of epidemic gastroenteritis associated with astrovirus, the first case reported in Japan, is described. Not only children (5–6 years of age), but also staff members of a kindergarten were affected. The virus particles detected in stools were 28–30 nm in diameter with a circular outline and had the characteristic starlike configuration which allowed identification as astrovirus. Significant immune responses to the virus were confirmed by immune electron microscopy. Out of 84 children, 43 (54.2%) were affected; the common symptoms were vomiting, abdominal pain, diarrhea, and fever. All the patients recovered completely within 48 hours. Occurrence of gastroenteritis due to contact with these patients was observed in 14 of 43 famil