OBJECTIVE: To investigate an outbreak of Pseudomonas aeruginosa (PA) hospital-acquired infections in neonates. METHODS: Incidences were assessed retrospectively in the neonatal care units of the Groupe Hospitalier Sud-Reunion, from January 2003 to September 2005. Environmental survey, audit of health care workers and case-control study were performed to reinforce staff training and to determine risk factors. RESULTS: Of 1432 neonates, 40 were infected (median gestational age: 29 weeks, median birth weight: 1195 g), accounting for an attack rate of 2.8%. Between January 2003 and January 2004, incidence rates were less than 2 infections per 1000 hospitalisation days. In the last trimester of year 2004, the incidence rose to 5.6 infections per 1000 hospitalisation days and PA was found in all ocular swabs, leading to diagnose an epidemic. However, it was only 3 months later, after 3 new deaths of very preterm neonates, that the implementation of control measures and an audit of health care practices focused on water utilisation ruled out the outbreak. The overall fatality rate was 25%, and of 71% in severe diseases (septicemia or pneumonia). The epidemic pattern argued for a common unique source. Two risk factors were identified by logistic regression: exposure to mechanical ventilation beyond 4 days (OR 3.3; CI 95%: 1.3-8.4) and very preterm birth (OR 2.7; CI 95%: 1.0-7.7). CONCLUSION: Our findings highlight the need for a close collaboration between neonatologists and hygienists to improve health care practices and surveillance.