Invasive meningococcal infections (IMI) are serious infections that most commonly affect young people. In France, the majority of cases occur sporadically. 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, describes the annual trends of the disease and its main characteristics, and evaluates the preventive measures implemented. The National Reference Center for Meningococci (CNR) participates in national surveillance and performs comprehensive phenotyping as well as antibiotic susceptibility testing on meningococcal strains received from all bacteriology laboratories. It contributes to the surveillance of potential epidemic clones through molecular typing of Neisseria meningitidis. This article presents the results of the analysis of IIM cases reported in France in 2004. (Introduction)