Although Nocardia farcinica surgical site infection outbreaks have been reported (though rarely), no source for these has been identified. From May 1992 through June 1993, 5 patients contracted N. farcinica sternotomy site infections following open heart surgery at hospital A. A case-control study comparing case-patients (n=5) with open heart surgery patients without subsequent sternotomy site infections (n=50) identified as risk factors diabetes (4/5 vs. 11/50, P<.02) and exposure to a particular anesthesiologist (anesthesiologist A; 4/5 vs. 9/50, P<.01). Four case-patients' isolates and a hand isolate of anesthesiologist A had an identical ribotype pattern (strain 1); the remaining case-patient's isolate and multiple isolates from anesthesiologist A's hands and home had a different ribotype pattern (strain 2). An intensified hand-washing regimen, barriers (gloves, gowns), and cleaning of anesthesiologist A's house were associated with termination of the outbreak. This is the first reported nosocomial N. farcinica outbreak to document the source and person-to-person transmission epidemiologically and molecularly.