Introduction: From April 3 to 7, 2000, four cases of meningococcal infection (MI) caused by serogroup W135, two of which were fatal, were reported among pilgrims returning from Mecca and their immediate contacts. The rarity of the strain in France, its affiliation with the clonal complex implicated in several epidemics in Europe and the Americas, and the high case fatality rate observed led the Directorate General of Health (DGS) to recommend, on April 8, chemoprophylaxis with rifampicin for all pilgrims and people living in their households. The French Institute for Public Health Surveillance (InVS) conducted an investigation to characterize the outbreak, track the spread of the strain within the population, and assess the impact of the measures implemented and the potential need for additional specific measures. Methods: A case was confirmed when a strain isolated after March 22 from a normally sterile environment was identical to the epidemic strain (W135, 2a: P1-2.5 – ET37 clonal complex). A case was considered probable when it occurred in a pilgrim or a contact of a pilgrim presenting either with clinical meningitis (purulent cerebrospinal fluid or purpura fulminans) or a W135 strain whose characteristics could not be determined. For each case, a standardized questionnaire, developed in collaboration with the European countries affected by the epidemic, was administered. Results As of November 20, 2000, 25 confirmed cases and 2 probable cases had been identified; 85% of the cases occurred during the first 7 weeks of the outbreak. The case fatality rate was 18%. Patients over 50 years of age accounted for 66% of cases (6/9) before April 9, 2000, and 17% of cases (3/18) after that date. Four patients presented with monoarthritis. No clusters of cases were identified. Four cases occurred among the 19,100 pilgrims (incidence rate: 21/100,000), 9 among people living at home, 7 among individuals who had direct contact with a pilgrim outside the household, and for 7 cases, no direct contact with a pilgrim was found. These 7 cases occurred after the third week of the outbreak. No cases occurred among individuals who had undergone rifampicin chemoprophylaxis. Eighteen cases occurred after the DGS recommendations were issued, 5 of which were among the population targeted by the measures. Conclusion: These data suggest that the epidemic strain is no different from other strains in terms of virulence and transmissibility. Eight months after the end of the pilgrimage, the number of cases linked to the epidemic remained limited in France. However, the characteristics of the most recent cases suggest that the epidemic clone continues to circulate in the general population. The DGS recommends that pilgrims traveling to the 2001 Mecca pilgrimage receive the quadrivalent A,C,W135,Y vaccine.