The current literature indicates that surgical-site infections significantly increase costs and length of stay. Nosocomial infections that are acquired after operative procedures increase mortality rates. Staphylococcus aureus is a major cause of surgical-site infections among patients, particularly patients who undergo cardiothoracic surgery. Patients who carry S aureus in their nares are at increased risk for surgical-site infections that are caused by this organism. Occasionally, health care workers who carry S aureus in their nares can cause outbreaks of surgical-site infections or other nosocomial infections. Persons who carry S aureus in their nares and have upper respiratory tract infections may spread this organism to numerous staff members and patients. Key measures for decreasing rates of these and other nosocomial infections include the appropriate use of prophylactic antimicrobial agents, surveillance and reporting of infections, and surveillance for clusters of infection caused by the same strain of S aureus and culture and surveys, when appropriate, to help identify infected health care workers. Additionally, surgical masks may prevent health care workers from inadvertent transmission of S aureus from their nares to patients' surgical sites.