Two outbreaks of postoperative wound infections due to organisms of the Mycobacterium fortuitum complex (Mycobacterium chelonei and M. fortuitum) occurred among patients who underwent open-heart surgery. In one hospital, 19 of 80 patients who underwent cardiac surgery within a 10-week period developed sternal infection with M. chelonei. In the second hospital, four of nine patients who underwent cardiac surgery within a two-week period developed sternal incisional infection with M. fortuitum. Although epidemiologic investigations uncovered factors that were significantly associated with the development of infection, the source of the infections could not be determined. The results of numerous cultures were negative, but because the investigations were conducted at least two months after many of the patients had had surgery, the materials in use at the time of the surgery were not available for culture. These results emphasize that physicians should be aware that rapidly growing mycobacteria may produce postoperative wound infections.