In France, surveillance of listeriosis is carried out by the National Reference Center for Listeria (CNR, Institut Pasteur, Paris), which collects and characterizes Listeria monocytogenes strains from microbiology laboratories, and through mandatory reporting (DO) by physicians to the Departmental Directorates of Health and Social Affairs (DDASS). For each reported case, Public Health Medical Inspectors (MISP) systematically supplement the DO with a questionnaire regarding the patient’s diet during the two months preceding the onset of symptoms. The DO and dietary questionnaires are then systematically sent to the InVS. The CNR informed the crisis unit on 12/29/99 of the existence of 4 cases of listeriosis occurring between 10/25/99 and 11/22/99 caused by Listeria monocytogenes serovar 4b and lysovar 2389:3552:2425: 14444: 3274: 2671: 52-108: 340, exhibiting the same DNA macrorestriction characteristics. A fifth and sixth case were subsequently identified on December 30, 1999, and January 5, 2000, respectively... The current system for monitoring listeriosis and investigating alerts made it possible to quickly identify the vehicle and source of the outbreak and to implement risk management measures. Nevertheless, this outbreak once again highlighted the need to strengthen public information efforts through all available means, including via healthcare professionals. (R.A.)