Passenger car collisions with other vehicles and with fixed objects were studied from a representative sample of fatal and injury-producing collisions collected according to a prescribed sampling plan. This paper describes our analysis of accidents involving restrained passenger car occupants who are fatally injured in collisions. Lateral collisions were found to be predominant, and both lateral and frontal collisions were associated with marked intrusion into the occupant compartment, causing direct, severe injuries to the head and chest of these occupants. Multiple severe injuries to more than one body region were common, and 90% of these victims died within one hour of the collision. The seat belt generally offered no protection to these fatally injured occupants. Reducing the incidence of fatal injury to properly restrained passenger car occupants will necessitate diminishing these very severe intrusion forces, especially from heavy trucks and fixed vertical hazards. For vehicle design modifications to be effective, it appears likely that roadway and roadside design and management must be included in the safety equation. Excessive speeds, inadequate traffic control, and unforgiving roadside hazards are playing a major role in the incidence of fatal injuries documented in this study.