The vascular anatomy of the pectoralis major muscle and overlying skin and subcutaneous tissue was investigated in seventeen cadaver specimens by cannulation of the arterial supply and injection of contrast medium. A rich anastomosis between the internal mammary artery and the pectoral branch of the thoraco-acromial artery and between the pectoral branch and the lateral thoracic artery was demonstrated. In 36% of cases a major axial cutaneous vessel, originating close to the thoraco-acromial artery, was shown to extend caudad. The lateral thoracic artery, in addition to the pectoral branch, contributed significantly to the vascularity of the pectoralis major muscle and was the main blood supply to the female breast. The skin overlying the muscle was abundantly supplied from the muscle vasculature. Both the major arteries were enclosed within the muscle's fascial envelope. A technique for developing a standard pectoralis major myocutaneous island flap is described. Our studies show that a hemichest flap incorporating all the skin of the chest over the muscle is feasible.