\s=b\In a series of 43 pectoralis major myocutaneous flaps (PMMF), five (12%) developed partial or total necrosis. The cause of necrosis was speculative in each case. To evaluate the problem, we studied the vascular supply to the PMMF, specifically, the lateral thoracic artery (LTA) and the pectoral branch of the thoracoacromial artery (TAA-PB). Ten aortic arch angiograms and 35 cadaver dissections were analyzed. The LTA and TAA-PB provided pedicles of comparable size in most cases, and in several the LTA was significantly larger than the TAA-PB. In one angiogram the TAA-PB was totally occluded, probably by atheromatous plaque. Peripheral vascular disease can affect myocutaneous flaps. We postulate that the LTA can nourish the PMMF by itself and sustain flaps that might otherwise develop necrosis.