Norwalk virus infection is the leading cause of non-bacterial epidemic gastroenteritis,which is common in adults and elder children,and can occur in all seasons. However,since no routine laboratory test is available,it can seldomly be definitely diagnosed clinically. From 20 to 24 in Oct. 2003,82 patients including 81 students and 1 teacher in an elementary school of Yuexiu district in Guangzhou city complained of vomiting,stomach cramp,diarrhea and fever. After detailed and repeated investigation on the spot by the CDC of Guangzhou and Yuexiu district,with the technological support from Guangdong CDC,Norwalk virus in patients' feces was identified by RT- PCR. This is the first confirmed incidence of collective acute gastroenteritis caused by Norwalk virus in Guangzhou.