Four adults among three unconnected groups of spectators at a rugby match developed invasive meningococcal disease four to five days after the match. Two died. All four cases were caused by serogroup C serotype 2a strains, genotype P1.5, P1.2. Although the route of transmission remains uncertain, the most likely explanation is that an asymptomatic carrier disseminated meningococci to at least four others in the course of an afternoon. Clusters among spectators at an event without other links between cases are very unusual.