Surgical treatment of patients with traumatic shoulder dislocations is usually successful, but soft-tissue surgery in patients with nontraumatic shoulder dislocation often fails to stabilize the joint. Previous studies have shown that decreased humeral head retroversion might be one cause of anterior shoulder instability. Eleven patients with anterior recurrent dislocations, five traumatic and six nontraumatic, and all with a small humeral head retroversion angle, have been operated on using a proximal humerus osteotomy to correct the abnormal anatomy. After surgery, the humeral head retroversion was normalized to a mean angle of 34 degrees. All shoulders became stable. External rotation increased 7 degrees on the average, and internal rotation decreased 10 degrees on the average. One year after surgery, shoulder function was excellent in all operated shoulders.