We retrospectively reviewed the results of rotational osteotomy that had been performed distal to the surgical neck of the humerus in twenty-two patients who had sustained an injury of the brachial plexus at birth. Eighteen patients had a lesion of the superior trunk of the brachial plexus (the fifth and sixth cervical nerve roots), and four had involvement of the entire brachial plexus. The patients ranged in age from four to seventeen years old (average age, ten years and three months old) at the time of the operation. The average duration of follow-up was fourteen years (range, two to thirty-one years).Preoperatively, the patients had been unable to perform self-care activities, such as grooming, feeding, and washing themselves, because of limited active external rotation or fixed internal rotation of the shoulder. All patients had decreased strength of the lateral rotator and abductor muscles and normal strength of the subscapularis and pectoralis major muscles. Radiographs showed some flattening of the humeral head, and four patients had posterior subluxation of the humeral head.A lateral rotational osteotomy of the proximal part of the humerus was performed between the insertions of the subscapularis and pectoralis major muscles. The site of the osteotomy was stabilized with catgut sutures in the periosteum in ten patients and with one or two staples in twelve. The extremity was immobilized in a plaster shoulder-spica cast for six weeks.At the latest follow-up evaluation, the average increase in active abduction was 27 degrees (range, 0 to 60 degrees) and the average increase in the arc of rotation was 25 degrees (range, 5 to 85 degrees). Supination of the forearm also had increased commensurate with the increase in external rotation. The appearance of the extremity had improved as well.