In 2008 and 2009, a major community-based hepatitis A outbreak, which initially affected a municipality in the Lille metropolitan area, spread widely across several districts of the Nord department. An epidemiological surveillance program was implemented to identify factors contributing to transmission and to adapt control measures, based on data from mandatory reporting. A case was defined as a person residing in the Nord department who presented clinical signs of acute hepatitis associated with positive serum anti-HAV IgM antibodies in 2008 and 2009. A total of 492 cases were reported to the Nord DDASS, including 157 cases occurring in 2008 and 335 in 2009. The geographic analysis identified 5 epidemic clusters, with the 3 main ones affecting the Denaisis, Valenciennois, and Lille metropolitan areas. The median age of cases was 9.5 years [min–max: 1.5–87]. The hospitalization rate was 28%, and one severe case was reported. The source of infection was linked to active person-to-person transmission within the family or close social circle (45% of cases), in communities living in poor sanitary conditions (26% of cases), and within childcare settings (17% of cases). The virological investigation revealed the complex circulation of genotype IA strains belonging to three phylogenetic clusters. In addition to strengthening the standard hygiene measures, controlling the outbreak required the large-scale implementation of individual and community vaccination strategies, in accordance with the recommendations of the High Council for Public Health dated February 13, 2009. This vaccination was fully funded by the DRASS. This episode illustrates the high epidemic risk of HAV and the value of vaccination around cases as a preventive measure complementary to the reinforcement of hygiene measures. (R.A.)