This new issue of the Health Surveillance Bulletin (BVS) takes a look back at the public health event that marked the 2009–2010 season—the 2009 influenza A(H1N1) epidemic—and, more specifically, at the epidemiological assessment conducted for the Aquitaine region. This assessment could not have been carried out without the support of all the professionals who worked tirelessly for several months to monitor this epidemic—linked to the emergence of the influenza A(H1N1)2009 virus—in the Aquitaine region. The InVS Regional Unit (Cire) in Aquitaine would like to take this opportunity to once again express its sincere gratitude to them. In the first part, this special BVS review outlines the surveillance system that was implemented, including its various phases and associated surveillance systems. The second part presents the quantitative assessment of the surveillance of individual cases, clustered cases, as well as severe cases and deaths, based on the various available data sources. The discussion is based primarily on a comparison of the outbreak in Aquitaine with that observed in mainland France. It is worth noting in particular that this outbreak occurred earlier than previous seasonal episodes, beginning in November. It is estimated to have affected nearly a quarter of the population (approximately 750,000 people in Aquitaine). While the illness was mild for the majority, a more severe clinical presentation was noted in some cases compared to seasonal influenza, and it affected a younger population. This health event, rich in lessons, should enable all stakeholders in the region’s health surveillance system—now part of the new structure of the Aquitaine Regional Health Agency (ARS)—to contribute to strengthening existing surveillance systems and improving mechanisms for preparing and implementing control and prevention measures.