Whereas anterior dislocation of the shoulder is very common, posterior dislocation occurs in less than 2% of all cases. The diagnosis of posterior shoulder dislocation - especially in locked position - is difficult. The exact knowledge of the position of the humeral head within the shoulder joint is extremely significant, as the following case shows. The posterior shoulder dislocation was primarily recognized and treated correctly, while radiographics after reduction were misinterpreted. In this paper diagnostic and therapeutic measures are described.