In Réunion, the influenza surveillance system made it possible to track the epidemiological dynamics of the outbreak linked to the emergence of the 2009 pandemic A(H1N1) virus. This system relied primarily on a network of sentinel physicians, combined with virological surveillance, as well as monitoring of severe cases and deaths. The data provided were analyzed and disseminated on a weekly basis. The first imported case was confirmed on July 5, 2009, in a traveler returning from Australia, and the first locally acquired cases were reported on July 23. The epidemic peaked within five weeks, and the duration of the outbreak was nine weeks. The pandemic virus very quickly supplanted the seasonal viruses that had begun to circulate, and the attack rate for symptomatic cases of infection with the 2009 A(H1N1) virus is estimated at 12.85%. The hospitalization rate was 32 per 10,000 estimated cases, and 24 people developed severe illness requiring admission to the intensive care unit. Among the death certificates received by the Regional Directorate of Health and Social Affairs, 14 mentioned influenza, including seven for which the presence of the pandemic virus was biologically confirmed. These deaths occurred in individuals significantly younger than those typically observed in Réunion for seasonal influenza. Overall, the epidemic was of similar intensity and severity to that of seasonal influenza on the island of Réunion. (R.A.)