Posterior sternoclavicular dislocation is a relatively uncommon lesion, but must always be considered in the event of trauma to the scapulothoracic area in which initial radiology does not show signs of fracture. Its diagnosis and treatment must be carried out promptly because of the possible serious complications that may occur through the clavicle compressing nearby structures. The authors report two cases, which were diagnosed by CT-scan. In the first case, treatment consisted in orthopedic reduction, while in the second case open reduction and fixation with Kirschner wires was required. The result was satisfactory in both cases, and the patients remain asymptomatic three and five years after trauma.