Klebsiella pneumoniae resistant to third-generation cephalosporins and gentamicin was isolated from two patients in a paediatric intensive care unit within a two-week period. The double-disc diffusion test indicated the presence of an extended-spectrum beta-lactamase (ESBL). The unit was closed to admissions, and stringent infection control procedures were implemented. Environmental screening and screening of staff and patients on the unit were commenced. Two weeks later, K. pneumoniae with an identical antibiogram was isolated from the urine of a patient in a different ward. Blood-culture isolates possessed the K16 antigen, while the urine isolate was non-typeable. The isolates were shown to be similar when banding patterns of XbaI chromosomal DNA digests were compared. The resistance to the extended-spectrum cephalosporins was shown to be transferable in association with a large plasmid > 98 mDa. Resistance to gentamicin always co-transferred with beta-lactamase resistance and appeared to be encoded by the same plasmid.