After the introduction of routine treatment for every nasal carrier of methicillin-resistant Staphylococcus aureus, active follow-up surveillance for nosocomial methicillin-resistant S. aureus infection was conducted for 5 years in an intensive care unit of a tertiary-care teaching hospital. There was a significant decrease in the incidence of nosocomial methicillin-resistant S. aureus infection during the later years of follow-up. Decolonization of nasal carriers of methicillin-resistant S. aureus is probably associated with such findings.