A statistical algorithm was used to identify potentially important clusters among nosocomial infections reported each month by 7 community hospitals. Epidemiologic review and on-site investigations distinguished outbreaks of clinical disease from factitious clusters. In 1 year, 8 outbreaks were confirmed. They involved 82 patients—approximately 2% of patients with nosocomial infections and 0.09% of all discharges. One true outbreak occurred for every 12,000 discharges—at least 1 outbreak per year for the average community hospital. Five (63%) outbreaks were recognized independently by the hospitals' infection control personnel. Four (50%) resolved spontaneously; the hospitals' own control measures were necessary in 2; and 2 resolved only after an outside investigation. Organized surveillance appears necessary to detect some outbreaks, and control measures are needed to stop many. Since, however, outbreaks account for such a small proportion of nosocomial infections, infection control programs should be sufficiently staffed and managed so that most of the effort is directed toward the surveillance and control of endemic infection problems, but with adequate resources remaining to respond to outbreaks when they occur.