OBJECTIVE To investigate an outbreak of carbapenem-resistant Pseudomonas aeruginosa (CRPA) in a urology ward. METHODS Patients infected or colonized with CRPA were prospectively identified by daily laboratory surveillance. Routine infection-control measures were reinforced, disinfection protocols were revised, and a surveillance program was set up, analyzing cross-transmission in the nursing ward and environment cultures from urology wards and the operating theater. CRPA isolates from clinical and environment samples were studied by pulsed-field gel electrophoresis (PFGE), following XbaI and SpeI restriction. RESULTS From February 1998 to September 2000, 59 adult urology patients were colonized or infected by CRPA. All patients had been operated on prior to identification of the CRPA isolate and 79% of these procedures were performed in the same cystoscopy room. No patients had received prior carbapenem therapy. No cross-transmission was detected, and environment cultures from the urology ward and theater were negative except for five samples collected in the cystoscopy room. PFGE identified a single clone in the isolates from different patients and the environment samples. CONCLUSIONS The PFGE analysis indicated that the CRPA outbreak resulted from the contamination of the cystoscopy room via an unsealed drain. The outbreak ended when the drain was sealed.