From July 1995 to November 1996, multi-resistant Pseudomonas aeruginosa O11 was isolated from 36 patients admitted to a neurosurgery intensive care unit. The strain was resistant to ticarcillin, ceftazidime, imipenem, gentamicin and ciprofloxacin, and susceptible to amikacin. Nine patients were colonized only; the remaining 27 patients had at least one infected site (17 urinary infections, 10 pneumonias and four with sinusitis). P. aeruginosa O11 with the same resistance pattern was isolated from tap water. The strain was also cultured from enteral nutrition solutions given to two infected patients. DNA macrorestriction analysis with XbaI established the similarity of the isolates from patients, tap water and solutions. The outbreak was controlled after reinforcement of isolation procedures for infected patients, changing the mode of enteral nutrition and replacement of all sinks in the unit. The sinks were presumably the main source of P. aeruginosa during this outbreak, via the hands of the nursing staff or nutrition solutions contaminated with tap water.