An epidemic of surgical wound infections caused by group A Streptococcus affecting 18 patients in a community hospital was studied. Onset of symptoms shortly after surgery (median time, 16 hr) in 17 patients suggested acquisition of infection in the operating room, and a case-control investigation linked the presence during surgery of one particular nurse with postoperative streptococcal infection. During the first month of the epidemic, the nurse had streptococcal cellulitis of the finger and may thus have directly contaminated wounds or dressings. However, the last six wound infections occurred after her skin lesions had resolved and after nasopharyngeal and skin cultures were repeatedly negative for group A streptococci. Subsequent investigation showed that the nurse was colonized vaginally with group A streptococci of the same M and T types found in the infected patients and that this organism was disseminated into her immediate environment by airborne or droplet spread. Vaginal as well as rectal carriers of streptococci should be sought whenever outbreaks of streptococcal wound infection in which a cutaneous or nasopharyngeal carrier cannot be readily identified.