A 3-year prospective study examined 76 frontal (F) and 45 lateral (L) motor vehicle crash (MVC) patients with regard to seatbelt restraint use and occupant compartment contact and intrusion injuries. These 121 MVC victims with multiple injuries (39 belted B and 82 non-belted NB), admitted to a level I trauma center, were studied by accident reconstruction and medical data analysis. They had a MVC mean impact velocity (delta V) of 30 +/- 11 mph and an injury Severity Score of 29 +/- 12. Proper restraint use reduced brain injury in F MVCs (30% FB vs. 47% FNB) but had no effect in L MVCs (63% LB vs. 30% FB p < 0.06). Belt use did not protect against lung, liver, spleen, pelvis, or lower extremity (LE) injury. These appeared to be more a function of crash direction, with LE injuries higher in F crashes (p < 0.04) and pelvis injuries (p < 0.001) higher in L crashes. In FB crashes, however, properly used safety restraints were the primary cause of bowel or colon injuries (p < 0.006). Belts did not prevent thoracic or abdominal solid organ injuries in L crashes. Contact-intrusions (CI) of the car occupant compartment in F crashes were the main cause of brain (A-pillar), lung and liver (steering wheel and instrument panel), and LE (toepan) injuries; but in L crashes, side-door CI caused lung, aorta, liver, and pelvic injuries. In contrast, contact-only (CO) injuries of the steering assembly were mainly responsible for injuries to the lung, heart, and liver in F crashes, and side-door CO for lung, liver, and spleen injuries in L crashes. Deaths and complications after injury were higher among F MVC occupants, or when delta V was > or = 30 mph. Hospital and professional costs reflect the complex care needed for victims of multiple injuries: FB, $99,000; FNB, $95,000; LB, $75,000; LNB, $79,000; total, $10.7 million. Present vehicle safety standards are not adequate, and structural design changes are needed to improve restraints and protect occupants from intrusion-related injuries.