Pseudomonas aeruginosa (PA) is a common cause of severe nosocomial infections (NIs). The emergence of new resistance phenotypes is making the treatment of these HIs increasingly difficult. PA infections may be reported to the Departmental Directorate of Health and Social Affairs (DDASS) and the Coordination Center for the Control of Hospital-Acquired Infections (CClin) due to their rare or unusual nature or in the event of the patient’s death. Analysis of HAI reports received by the French Institute for Public Health Surveillance (InVS) from August 1, 2001, to June 30, 2006, confirms the prevalence and severity of PA-related HAIs. Of the 3,520 reports received during this period, 332 (9%) were reports of PA-related NI, 70 of which were cluster cases. Respiratory infections (29%), urinary tract infections (21%), and bacteremias (20%) accounted for nearly three-quarters of the sites of infection. The case-fatality rate associated with these reported infections was high (21%). One-quarter (24%) of the strains characterized by antibiotic susceptibility testing were resistant to all antibiotics recommended for the treatment of PA-associated NI (except colistin). The description of two clusters of cases illustrates the methods of investigation and prevention of PA-associated NI. (R.A.)