Posterior shoulder dislocation is a relatively uncommon event, with an incidence of 1% to 4% of all shoulder dislocations. Because of the infrequency of this condition, the diagnosis is often missed, with significant consequences to the patient Injury in the athlete is usually from a direct blow or fall onto an outstretched arm. After such an injury, symptoms may be confused with a shoulder contusion or rotator cuff injury. Significant complications such as chronic posterior dislocation and degenerative disease of the shoulder can occur if the diagnosis is missed. A careful history and physical examination, complete radiographic evaluation, and a high level of suspicion are required to identify posterior shoulder dislocation. Treatment consists of prompt closed reduction, or operative repair if this is unsuccessful.