Patients with surgical site infections (SSIs) who underwent surgery during the period of September 1997 through December 1999 and January through July 2001 were retrospectively studied to compare patients infected with methicillin-resistant Staphylococcus aureus (MRSA) with those infected with organisms other than MRSA. Of patients with SSI who had known culture results, 77 (28.5%) of 270 had cultures that yielded MRSA. On univariate analysis, age of >or=70 years, duration of surgery of >or=4 h, duration of postoperative antibiotic treatment of >1 day, and discharge to a long-term care facility (LTCF) were significantly associated with MRSA SSI (P<.05 for all). On multivariate analysis, only discharge to an LTCF (odds ratio [OR], 2.3; P=.04) and duration of postoperative antibiotic treatment of >1 day (OR, 2.0; P=.03) were significantly associated with MRSA SSI; there was also a trend toward MRSA SSI being associated with use of a surgical drain for >1 day (P=.078). Postoperative factors may play a more important role in the causation of MRSA SSI than has previously been appreciated.