An outbreak of 3 cases of invasive meningococcal disease occurred in a secondary school on 2 campuses in Victoria. Despite having only one isolate (a C.2a:nst strain), meningococcal DNA was identified by polymerase chain reaction (PCR) in early culture-negative blood specimens of the other 2 cases. Both were subsequently shown by PCR to be capsule serogroup C by PCR. An committee was formed to manage the response to the outbreak. Chemoprophylaxis was offered to family and children who had been in close contact with the cases. As one strain had been confirmed as being of a vaccine-preventable group, vaccination was offered to the whole school community as well as the families of cases. The direct costs of the outbreak to public health, which would have been identical whatever the causative serogroup, was $8,178. Vaccine charges accounted for most of the additional $56,941 cost of vaccinating the target group of 1600 students, staff, and families. No further cases have been associated with this outbreak.