Lyme disease is transmitted through the bite of ticks infected with Borrelia. It then progresses through several successive stages. The primary stage is characterized by a migratory, ring-shaped skin rash (erythema migrans, or EM) centered on the tick bite, which appears within days or a month after the bite and resolves spontaneously. In the absence of appropriate antibiotic treatment at this stage, secondary and tertiary neurological, rheumatological, cutaneous, or cardiological manifestations may occur. In 2000, a study by the French Institute for Public Health Surveillance (InVS) aimed at determining priorities in the understanding, prevention, and control of non-foodborne zoonoses classified Lyme disease as a priority due to its emerging nature and potential severity. However, epidemiological data on Lyme disease available in France were scarce. The main data came from a prospective survey of Lyme disease cases diagnosed by volunteer general practitioners in the Sentinel Network in 1998. Based on 86 recorded cases, these data provided estimates of incidence rates by region. Alsace appeared to be the region with the highest incidence rate (86 cases per 100,000), followed by Limousin (42 per 100,000) and Lorraine (34 per 100,000). In this context, and given the local concerns expressed by physicians and, at times, elected officials or the public, studies were successively initiated by the Interregional Epidemiology Unit (CIRE) East in Alsace, by the CIRE Center-West in Limousin, and by the CIRE Rhône-Alpes in Rhône-Alpes.