Invasive meningococcal infections (IMIs) are serious infections that most often affect young people who appear to be in good health. In France, the majority of cases occur sporadically. Despite improvements in treatment options, the case-fatality rate and the rate of serious early sequelae from IMIs remain high. Surveillance of IIM is one of the missions of the French Institute for Public Health Surveillance (InvS). It enables the detection of clusters and increases in incidence, the description of the annual trends of the disease and its main characteristics, and the evaluation of the preventive measures implemented. This article presents the results of the analysis of data from the mandatory reporting of IIM collected for the year 2003. (R.A.)