Practically all reports in the literature emphasize the frequency with which posterior dislocation of the shoulder is unrecognized clinically and roentgenographically. Most reports, however, do not discuss the associated fractures of the humeral head which are present in practically all cases of posterior dislocation. Identification of a fracture involving the medial portion of the humeral head is probably the most important roentgenographic clue to the diagnosis of a posterior dislocation, and yet such fractures are often unrecognized because in many instances their appearance is atypical or their importance is unappreciated and minimized. Identification of such a fracture must be considered presumptive evidence of a posterior dislocation and is an absolute indication for special studies in the axial projection. An unrecognized posterior dislocation, especially when associated with fracture, results in destruction of the humeral head and joint surface, and functional impairment of the shoulder girdle and...