An outbreak of nosocomial infections by Flavobacterium meningosepticum in a neonatal intensive care unit is described. During a period of eleven weeks two patients presented with septicaemia and meningitis. In addition, nine patients were found to be colonized and three of these neonates developed septicaemia. The infected patients were treated with clindamycin and piperacillin. All the patients survived, but the neonates with meningitis developed hydrocephalus. An extensive bacteriological screening of the staff was negative, but in the ward environment, F. meningosepticum was found around sinks, on rubber stoppers for milk bottles and on "cleaned" teats. Several infection control measures were instituted. Established routines were revised, with particular emphasis on the handling of objects containing or in regular contact with water.