Introduction - The Ardennes department has one of the highest annual incidence rates of leptospirosis in metropolitan France. This study, conducted at the request of the Departmental Directorate of Health and Social Affairs (DDASS), aims to adjust the current prevention measures as necessary. Methods - To assess the significance of the observed excess incidence, data from the National Reference Center (CNR) for Leptospirosis were analyzed from 1996 to 2005, and factors likely to explain this phenomenon were investigated (surveillance bias, risk factors). Results - The completeness of leptospirosis case reporting to the CNR is 100% in the Ardennes. Diagnostic practices (high awareness among physicians, coexistence of Hantavirus infection, recall of suspected cases for a second serology test) improve the sensitivity of the disease detection system. The contribution of various risk factors was also highlighted: rurality, water-based recreation, climate, hydrology, and rodents. Discussion-Recommendations - This study allows the observed incidence to be attributed to a combination of multiple factors. The application of national recommendations must therefore be strictly maintained. However, no new recommendations appear to be necessary. (R.A.)