On August 28, 2003, the Departmental Directorate of Health and Social Affairs (DDASS) of Vienne reported five cases of Legionnaires' disease diagnosed over a two-day period to the Interregional Epidemiology Unit (CIRE) for the Center-West region. An investigation was then launched by the DDASS and the CIRE to confirm the epidemic nature of the outbreak, identify the common source(s) of contamination, and implement the necessary control measures. (R.A.)