In late May 2002, the Virology Laboratory at the Timone University Hospital (CHU) in Marseille notified the InVS of five confirmed cases of measles among young adults residing in Marseille. This article presents the results of an investigation coordinated by the Southern Interregional Epidemiology Unit (Cire) and designed to document the intensity of viral circulation in the PACA region. The purpose of this investigation was also to guide, where necessary, control measures, particularly vaccination efforts.