Staphylococcus aureus is a common cause of invasive infections, yet most assessments of prevalence are based on health care-based samples. We computed population-based estimates of nasal carriage of S aureus and risk factors for carriage, as well as population-based estimates of nasal carriage of methicillin-resistant S aureus (MRSA).We used the National Health and Nutrition Examination Survey (NHANES) 2001-2002 to estimate carriage of S aureus and MRSA for the non-institutionalized US population including children and adults.An estimated 86.9 million persons (32.40% of the population) were colonized with S aureus. The prevalence of MRSA among S aureus isolates was 2.58%, for an estimated population carriage of MRSA of 0.84% or 2.2 million persons. Among individuals with S aureus isolates, individuals aged 65 years or older had the highest MRSA prevalence (8.28%). Among all the racial/ethnic groups studied, Hispanics had the highest prevalence of colonization with S aureus but, when colonized, were less likely to have MRSA.This first nationally representative assessment of carriage of S aureus indicates that nearly one third of the population is currently colonized by this organism. Although the prevalence of MRSA remains low, more than 2.2 million people carry this resistant organism; thus, vigilance in promoting appropriate microbial transmission protocols should remain a priority.