A descriptive study was initiated in August 2007 following the occurrence of 9 clustered cases of hepatitis A in the Côtes-d'Armor department. A case was defined as a person in whom anti-HAV IgM antibodies were detected between July 1 and October 15, and who had been in the department during the six weeks preceding the onset of clinical symptoms. Environmental and microbiological investigations supplemented the study. A total of 111 cases were identified. Places of residence and stay were distributed around Lannion-Paimpol. The cases appeared in clusters; 83% reported jaundice and 26% had been hospitalized. Among the documented cases, 81% had eaten oysters and 87% had eaten raw shellfish (oysters, razor clams, clams, and cockles). Six cases associated with three outbreaks of HAV-related foodborne illness and 26 cases briefly present in the department had all consumed raw shellfish originating from or harvested near the same shellfish farm in Paimpol Bay. Two wastewater discharges into Paimpol Bay were identified. Environmental testing for HAV remained negative. Viral RNA was detectable in 68 serum samples: 66 genotype IIIA sequences were homologous. Mandatory reporting enabled early detection of the outbreak. Consumption of raw shellfish from the same shellfish farm was the most likely cause of contamination in these cases. Risk analyses specific to each shellfish farm and real-time information on sanitation system malfunctions should complement local authorities’ sanitation efforts. (R.A.)