Invasive meningococcal disease (IMD) is a feared illness due to its sudden onset—most often in young children or adolescents—its high case-fatality rate, the risk of serious long-term complications, and the epidemic potential associated with certain strains. Between 700 and 1,000 cases occur each year in France, primarily meningitis and meningococcemia. The overall case-fatality rate is approximately 12%. Most cases are sporadic and, as in most industrialized countries, are associated with different genotypes of Neisseria meningitidis, among which serogroups B, C, and W135 predominate. Over the past 10 years, the overall incidence rate of IIM has risen from 0.8 to 1.5 cases per 100,000 inhabitants (with a peak in 2003, partly due to the broadening of the case definition), and serogroup B accounts for 50 to 75% of cases, depending on the year. In early 2003, the French Institute for Public Health Surveillance (InVS) was alerted to an increase in the incidence of IIM in Seine-Maritime. A similar situation had already been the subject of a specific investigation in 1997. The average annual incidence rate of IIM in Seine-Maritime, which was 0.8 per 100,000 inhabitants before 1996, rose from 1.2 during the 1997–2002 period to 3.0 during the 2003–2006 period—a rate nearly twice as high as in the rest of France. This hyperendemic situation is linked to a significant increase in serogroup B IIMs and, more specifically, to the circulation of a serotype 14 strain of subtype P1.7,16 belonging to the ST-32 clonal complex. The recent epidemiological characteristics (2003–2006) of IIM, particularly those associated with the B:14:P1.7,16 strain, in the Seine-Maritime department and other departments in France are presented below.