While seat belt usage significantly decreases mortality and morbidity from traffic accidents, specific injuries may also occur. Two cases are described in adults where the wearing of three point restraints (shoulder-lap belts) in a serious high-speed vehicle accident resulted in fatal injuries to both a driver and a passenger. 'Mirror image' fractures of the sternum, rib cage and clavicles, with separation of the two halves of the rib cages and underlying trauma to the hearts and thoracic aortae resulted in death in both victims. Profound life-threatening internal injuries may be caused by seat belts in the absence of significant cutaneous injury. The pattern of internal trauma can also be useful in determining whether a seat belt was worn at the time of the accident, and on which side of the vehicle the deceased was sitting.