While shoulder dislocations are a common injury, dislocation in the posterior direction is unusual and often missed clinically. A traumatic posterior shoulder dislocation can be caused by a direct blow to the anterior shoulder or if a posteriorly directed force is axially applied through the forward flexed arm. A posterior shoulder dislocation can occur after a violent muscle contraction induced by an electrical shock or grand mal seizure. Posterior shoulder dislocations are commonly associated with posterior glenoid rim fractures and anterior compression fractures of the humeral head. This diagnosis should not be missed if a complete physical and radiographic exam are properly performed.