One hundred sixty-eight pectoralis major muscular and myocutaneous flaps performed at the University of Texas M. D. Anderson Cancer Center during the past five years were reviewed retrospectively to determine complication rates following operation and to evaluate the effect of risk factors such as smoking, obesity, sex, previous radiotherapy, and tumor stage on the incidence of such complications. The overall rate of complications was 63%; however, most of these complications were self-limited, and the rate of total flap loss was only 2.4%. The risk of a complication developing was increased slightly in patients who smoked cigarettes and in patients with larger tumors. Obesity and previous radiotherapy had no effect on complication rates. Women who underwent pectoralis major myocutaneous flaps had a higher rate of flap necrosis than did men, presumably because of the interposition of breast tissue between the muscle and the skin paddle. In patients who had muscle flaps (without skin paddles), sex had no influence on complication rates. In all groups of patients, flaps consisting of muscle alone had fewer complications than did flaps with a cutaneous component.