In May 2007, several cases of acute gastroenteritis (AGE) were reported among residents and staff at a nursing home for dependent elderly individuals (Ehpad) to the health authorities in the Var department, and an investigation was launched. A case of AGE was defined as a person with diarrhea or vomiting or abdominal pain, with or without a fever >38 °C. Data were collected using a standardized questionnaire. Stool cultures were performed to detect pathogenic bacteria, rotavirus, and adenovirus. The nursing home housed 58 residents and employed 32 staff members. From April 27 to May 7, 2007, 40 cases of GEA were recorded. The attack rate was 44%, higher among residents (53%) than among staff (28%). The course of the illness was favorable, with no hospitalizations. No factors that could have contributed to the outbreak were identified. A strain of norovirus, genogroup I, Chiba genotype (GGI-4), was isolated from stool cultures in one resident and one staff member. In the municipality, bacteriological water analyses and chlorine levels were within acceptable limits. An AGE outbreak occurred in a nursing home. The Group I norovirus strains identified support the hypothesis that the same virus affected both residents and staff. Preventive measures, implemented on May 1, limited the spread of the outbreak, which had spread due to the very high contagiousness of noroviruses. Residents eating lunch together and moving about the floors, as well as staff members, contributed to this spread. At the start of the outbreak, the prevalence rate among staff was higher than among residents (15% vs. 6%). This underscores that when cases of gastroenteritis emerge, rigorous hygiene measures must be implemented very quickly to limit the onset of an outbreak. (R.A.)