Leptospirosis is a zoonotic disease widespread throughout the world, caused by the bacterium Leptospira interrogans, which is currently classified into 23 serogroups. In metropolitan France, it affects 300 to 400 people per year, representing an annual incidence of 0.4 to 0.5 per 100,000 inhabitants. Aquitaine is one of the metropolitan regions where the incidence is consistently among the highest. During the summer of 2003, the Dordogne department also experienced a resurgence of cases compared to previous years. In France, leptospirosis is recognized as an occupational disease but has not been subject to mandatory reporting since 1986. Its epidemiological surveillance currently relies on serology requests submitted to the National Reference Center for Leptospira (CNRL). Although not exhaustive, this surveillance allows for the tracking of temporal trends. In 2004, the Aquitaine Interregional Epidemiology Unit (Cire), in collaboration with the French Institute for Public Health Surveillance (InVS), launched a prospective and descriptive study of leptospirosis incidence in Aquitaine covering a period of at least two years. The objectives of this study are to improve the identification and characterization of cases, to detect and investigate clusters of cases, and to assess the feasibility and relevance of classifying leptospirosis as a notifiable disease (MDO).