This article presents an investigation conducted to describe the extent and characteristics of clusters of "Methicillin-resistant Staphylococcus aureus" (MRSA) cases in the Côtes-d'Armor department. The investigation combines a retrospective case search covering the period from October 1999 to December 2001 with a prospective search beginning in January 2002. It confirms the emergence of community-acquired MRSA infections in France. The combination of methicillin resistance and a virulence factor (LPV) poses a potential risk of severe complications when the infection is located elsewhere than on the skin, particularly in the lungs. Studies must be conducted to characterize these infections and identify appropriate control and prevention measures.