The duration of colonization with methicillin-resistant Staphylococcus aureus is not well defined. During 1564 admissions after a clinical culture or surveillance test positive for methicillin-resistant Staphylococcus aureus, we retested patients for methicillin-resistant Staphylococcus aureus colonization. During the first year after the positive culture result was obtained, 48.8% of the patients (95% confidence interval, 45.8%-51.7%) remained colonized; at 4 years, 21.2% of the patients (95% confidence interval, 13.1%-31.4%) remained colonized.