A subcoracoid pectoralis major muscle transfer is an option for the treatment of irreparable subscapularis deficiency. Subscapularis deficiency is a significant source of pain, reduced strength, and instability in the shoulder. A pectoralis major transfer may be indicated in patients with subscapularis deficiency in whom previous surgical repair has failed or who are deemed to have an irreparable tear, patients with recurrent glenohumeral instability and subscapularis deficiency after a failed instability repair, and patients with chronic anterosuperior instability after previous prosthetic replacement. The pectoralis major tendon is detached from its insertion on the humerus and transferred in the subcoracoid position. The musculocutaneous nerve is dissected free from the undersurface of the conjoined tendon. The pectoralis major is then transferred deep to the conjoined tendon and superficial to the musculocutaneous nerve. A pectoralis major transfer is then attached to the greater tuberosity of the humerus. This appears to be an effective option for patients with the difficult problem of irreparable subscapularis deficiency as well as anterosuperior instability. It has a low complication rate and a high degree of satisfaction.