Severe infections caused by Pseudomonas aeruginosa are uncommon in patients infected with HIV. These infections are usually recurrent, bear a poor prognosis and their potential for nosocomial transmission is questioned. From May 1991 to December 1994, a total of 2,739 admissions were recorded at the VIH Unit in our hospital. Seven of those patients suffered 9 episodes of P. aeruginosa bacteremia (3.28 episodes/1,000 admissions). All cases were acquired nosocomially. The mean CD4 count was 30.7 cells/ml. Mortality associated with Pseudomonas aeruginosa bacteremia was 43%. With molecular typing techniques homologies over 98% were demonstrated for the two episodes in patient 4 and the episode in patient 3 (very close in time, 1993) and almost 99% between the isolate from patient 7 and the two isolates (identical) from patient 6. The other three isolates had relationship (to themselves and to the other isolates) lower than 97%. Our findings suggest that patient-to-patient transmission of severe infections caused by P. aeruginosa in patients with AIDS.