In late September 2004, a general practitioner in southwestern France reported several cases of hepatitis A that had occurred since July 1 in several neighboring municipalities, all of which were served by the same water supply system. An investigation was conducted to confirm and describe the outbreak and generate hypotheses regarding the mode of transmission of the disease in order to implement appropriate control and prevention measures. A total of 11 cases of hepatitis A, including 10 confirmed cases, were identified between July 1 and October 31, 2004, in five neighboring municipalities. Nearly half of the cases had attended village festivals. While all cases had consumed tap water, no common food source was identified. Two cases worked at the same food establishment that had prepared dishes for some of the village festivals. The environmental investigation and microbiological analyses of the water system revealed no failures that could explain waterborne contamination. Strain typing was performed by the CNR on 8 serum samples, all of which were found to be the same strain. The study confirmed the outbreak and ruled out contamination of individuals via the water supply. The homogeneity of the strains and the pattern of the curve supported a common, point-source of contamination. The hypothesis of HAV transmission by a contaminated food handler seemed the most likely, although this could not be fully verified (recall bias during the food survey, lack of strain typing of the food handlers). The main recommendations focused on improving good hygiene practices in food establishments by veterinary services and, more specifically, on strengthening health inspections in bakeries and pastry shops. (R.A.)