Introduction - Following the emergence of the 2009 influenza A(H1N1) virus, an alert and surveillance system was established by the French Institute for Public Health Surveillance (InVS). This article presents an epidemiological overview of influenza activity in mainland France during the 2009–2010 pandemic season. Method - The article is based on surveillance of individual cases (during the lockdown phase) and cluster cases, through networks of private practitioners and emergency departments, as well as the reporting of severe cases and deaths, in close coordination with virological surveillance. Results - Following the detection of the first cases of influenza A(H1N1)2009 in France on May 1, 2009, and the onset of viral spread during the summer, the pandemic wave occurred in France in late October and ended after a 10-week epidemic. It occurred earlier than the seasonal epidemics of the past 10 years, and it is estimated that between 13% and 24% of the population of metropolitan France was infected with this virus. While mortality linked to influenza A(H1N1)2009 appears limited, the profile of severe cases and flu-related deaths has changed, with the majority of cases involving people under the age of 65. (R.A.)