The objective of this study was to conduct an analysis from the 1993-2000 NASS database and determine the occurrence of head injuries (HI) as a function of restraint use to nearside occupants in lateral impacts. Data from NCAP crash tests conducted in our vehicle crashworthiness laboratory and elsewhere were used to determine the potential for HI. The NASS analysis indicated that the risk of sustaining HI of any severity was higher without than with belt use. The risk increased by four-fold in direct side impacts (3 and 9 o’clock). Although the overall risk of sustaining a very severe HI (AIS 4-6) was low (<5%), the significant morbidity (30%) associated with these injuries necessitates further research. While the thoracic trauma index was the same between drivers and passengers (66 versus 65), the head injury criteria varied by a factor of approximately two (635 vs 374) between the two occupants in NCAP tests. Passenger head contact with interior components (roofrail-C-pillar) was responsible for HI. A primary area of focus for side impact injury assessment and mitigation should be the struck side rear seat passenger. It may also be of value to better quantify HI metrics (e.g., rotational acceleration) by using a more biofidelic head-neck system in NCAP tests to advance injury mitigation strategies.