The occurrence of extended-spectrum beta-lactamase producing enterobacteria (ESBLE) has been prospectively surveyed in a neurosurgical intensive care unit (ICU). Of the 47 patients examined, 8 were identified as faecal carriers, and 2 of them developed a subsequent urinary tract infection. ESBLE were also detected in the immediate environment of five colonized and/or infected patients. All isolates were Klebsiella pneumoniae of a particular biotype which exhibited a similar antibiotype and produced an SHV-4 type beta-lactamase. However, plasmid profiling and ribotyping revealed that strains isolated from seven patients of hall A were a single epidemic clone, whereas strains isolated from the eighth patient of hall B were different. Comparison between the characteristics of patients who carried an ESBLE during the surveillance period, and control patients who did not, showed that a recent surgery, and the length of ICU stay were significantly associated with the acquisition of ESBLE.