Abstract An outbreak of 12 cases of infection occurred over a 9-month period in a Regional Referral Neonatal Intensive Care Unit. The pathogen was a gentamicin- and multiply-resistant Klebsiella oxytoca (K55), of high virulence. Seven of 10 neonates with septicaemia died, the majority within 24 h of the onset of infection. Screening for the resistant klebsiella revealed that 64 (39 per cent) of 164 neonates became carriers and remained so throughout their stay. Hand carriage appeared to be a mode of crosscontamination and infection. Cohorting colonized neonates together with rigorous cross-infection control measures eliminated this organism from the unit after 29 weeks. There is evidence to suggest that in one case the infecting organism was acquired from a contaminated blood gas analyser. It is necessary to use incompatibility grouping and restriction endonuclease digestion for complete characterization of plasmids and their molecular weights. However, the finding that each isolate examined carried the same five plasmids as judged by co-electrophoresis on agarose gels, and expressed the same extent and degree of transferable antibiotic resistance provides evidence to suggest that this outbreak was due to spread of a resistant clone of K. oxytoca (K55).