Posterior dislocation of the sternoclavicular joint is a rare but serious and life-threatening injury. Case reports describing injury to mediastinal structures including the trachea, esophagus, and the great vessels from posterior displacement of the medial clavicle (1, 2, 3, 4, 5, 6) have been discussed in the literature. It is important that radiologists are aware of the limitation of plain radiographs in detecting posterior SCJ dislocation and and that they carefully evaluate the soft tissues with CT imaging to exclude mediastinal injury.