Of forty patients with forty-one locked posterior dislocations of the shoulder, the diagnosis had been missed by the initial physician in the majority. A motor-vehicle accident, a seizure, an alcohol-related injury, or electroshock therapy had caused the dislocation in these patients, and the average interval from injury to diagnosis was one year. Twenty-five of the forty-one dislocations had been diagnosed in less than six months. An axillary radiograph confirmed the diagnosis in all shoulders and demonstrated the approximate size of the impression defect. There were no associated displaced fractures of the humerus, but in twenty of the shoulders there was an undisplaced fracture of the proximal part of the humerus. The average length of follow-up was 5.5 years. For seven shoulders the deformity was accepted. Treatment in the others consisted of closed reduction, which was attempted in twelve shoulders and was successful in six of the twelve; transfer of the subscapularis tendon, which was attempted in nine shoulders and was successful in four; transfer of the lesser tuberosity, which was successful in all four shoulders that were so treated; hemiarthroplasty, which was performed in nine shoulders and was successful in six (the other three required revision); and total arthroplasty in ten shoulders, one of which dislocated postoperatively and was not treated. Once the diagnosis is established, the majority of patients with this lesion can be successfully managed.