Patients in a pediatric intensive care unit were placed with patients in an adult surgical intensive care unit (SICU) in a large, 12-bed room previously occupied exclusively by the adult patients. The occurrence of multiply resistant Staphylococcus aureus (MRSA) in pediatric patients increased from zero cases during the preceding 12 months to seven cases (p less than 0.001) for the 95 days that the units were combined. The rate of acquisition of MRSA by the patients in the SICU remained unchanged. Pediatric patients who acquired MRSA had longer lengths of stay (p less than 0.001) and underwent more surgical (p less than 0.01) and invasive procedures than did pediatric patients who did not acquire MRSA. Removal of the pediatric patients to their own unit returned their rate of MRSA acquisition to the previous low level.