In a sample of 1,567 traffic accidents, 65 fatal crashes were available for a complete description of the lesions. In 14 cases, a complete crash reconstruction could be made. In order to define an injury criterion, a relationship between injury severity in real crashes and dummy loading values in experimental tests, was determined. For research purposes, the body was considered as a three compartment system: 1. Bony skull and brain: the negative part of the elastic wave, was considered to be the injury originator. 2. Cervical spine: the relatively inelastic fibrous bonding at the atlanto-occipital junction appears to be selectively vulnerable to the shearing force. Fractures to members of the CO-C1-C2 complex are almost always the result of head contact. 3. Thorax, abdomen, and pelvic contents: steering system intrusion is observed to play a significant role in the incidence of thoraco-abdominal injuries.