Introduction.—On July 28, 2009, a cluster of cases of the new influenza at a vacation center in the Alpes-de-Haute-Provence region was reported to Cire Sud. An epidemiological and biological study was conducted to identify the source of the infection and estimate the prevalence of the new virus. Methods.- The center hosted 94 children aged 6 to 14, divided into five age groups, and 28 adults. A probable case was defined as a person who stayed at the center between July 20 and 31 and presented with a systemic symptom (fever or malaise) associated with a respiratory symptom (cough or shortness of breath). Nasal swabs were collected and RT-PCR tests for influenza A and influenza A(H1N1)2009 were performed to biologically confirm the cases. Results.- The overall attack rate was 37% for possible cases and 21% for confirmed cases. All possible cases had presented with a cough, and 82% had at least one febrile episode. In both children and adults, gender and age were not factors associated with the onset of the disease. Attack rates varied by group, and the risk of developing the disease was significantly higher among 11- to 13-year-olds than among 6- to 8-year-olds (RR = 3.02). The virological study showed that five asymptomatic individuals were carriers of the virus. Three of them subsequently became paucisymptomatic, and two remained completely asymptomatic. Discussion/Conclusion.—This study confirmed the occurrence of an outbreak of the new influenza A(H1N1)2009 at this vacation center. It highlights the presence of asymptomatic carriers and the influence of age-specific behaviors on the spread of the virus within a susceptible population. These results reinforce recommendations for the early implementation of preventive measures in a community of children. (R.A.)