Posterior dislocation of the sternoclavicular joint is a rare and emergent injury. Diagnosis is often missed or delayed. Treatment is challenging because of the joint's inherent instability. This article presents a 15-year-old adolescent who experienced a traumatic posterior dislocation of his right sternoclavicular joint that was treated successfully with open reduction and joint reconstruction using the ipsilateral subclavius tendon autograft. At one-year follow-up, the patient was asymptomatic, with a stable sternoclavicular joint and full range of motion of his right shoulder.