Posttraumatic bacterial mediastinal abscess resulting from closed blunt trauma without penetrating injury or tracheal or esophageal rupture is, to our knowledge, previously unreported. We report a case of a patient injured in a motor vehicle collision that resulted in closed blunt chest trauma and mediastinal abscess 14 days after injury. Initial chest roentgenogram revealed a widened mediastinum. Computed tomographic scan of the chest revealed comminuted fractures of the upper sternum, manubrium, and the 3rd and 4th left anteriolateral ribs and a retrosternal hematoma. Transesophageal echocardiography was negative. The patient was dismissed 2 days after injury and returned to the hospital 14 days after injury with a fluctuant, pulsatile, upper midline chest wall and anteriolateral chest wall staphylococcal abscesses. The abscesses were drained and the sternomanubrial wound debrided in stages. The mediastinal defect was reconstructed with a pectoralis major muscle flap. This most likely represents bacterial seeding of the mediastinal hematoma from a distant source.