The objective of this study was to determine whether use of mupirocin nasal ointment for perioperative eradication of Staphylococcus aureus nasal carriage is effective in preventing the development of surgical site infections (SSIs). A randomized, double-blind, placebo-controlled design was used. Either mupirocin or placebo nasal ointment was applied twice daily to 614 assessable patients from the day of admission to the hospital until the day of surgery. A total of 315 and 299 patients were randomized to receive mupirocin and placebo, respectively. Eradication of nasal carriage was significantly more effective in the mupirocin group (eradication rate, 83.5% versus 27.8%). In the mupirocin group, the rate of endogenous S. aureus infections was 5 times lower than in the placebo group (0.3% and 1.7%, respectively; relative risk, 0.19; 95% confidence interval, 0.02-1.62). Mupirocin nasal ointment did not reduce the SSI rate (by S. aureus) or the duration of hospital stay.