Many bacterial and viral agents can cause encephalitis, but an etiological diagnosis is rarely established. The PMSI is the only ongoing source of information on these conditions. We analyzed PMSI data from 2000 to 2002 to review the current state of knowledge. Patients from mainland France with a diagnosis of encephalitis not associated with HIV infection were extracted from the database. Demographic, spatial, and temporal data, as well as details describing the hospital stay, were analyzed. For each year, approximately 1,200 patients were recorded, originating from all departments, and hospitalized in equal numbers in general and university hospitals. The mean age was 38 years, and the majority were men. On average, 80% had no etiological diagnosis. The most common etiological diagnosis was herpes encephalitis in adults and VZV encephalitis in children. These data provide the basis for a national study on encephalitis. This study will last one year and will include patients from all participating centers in 2007.