Between January 21 and February 16, 2000, the occurrence of three cases of meningococcal meningitis of the antigenic serotype B:15: P1-7,16 and one suspected case in a town of 12,000 inhabitants in the Jura department led health authorities to decide to implement population-wide chemoprophylaxis in two neighborhoods. This study describes the context in which the cases occurred, the decision-making process that enabled crisis management, and the procedures for implementing the expanded prophylaxis. (R.A.)