Of the 222 flight helmets retrieved from Army aircraft accidents during 1971-79 under the Aviation Life Support Equipment Retrieval Programs, 175 were SPH-4 helmets that were analyzed for physical damage and for the relationship of damage to injury sustained by the wearer. This analysis showed that lateral impacts resulted in a significantly higher rate of serious injury (AIS greater than or equal to 4) than impacts to other regions (68% versus 46%, p less than 0.001) Lateral impacts yielded a higher rate of basilar skull fracture than impacts to other areas of the helmet (46% versus 18%, p less than 0.001). It is concluded that lack of energy-absorbing material in the lateral portions of the helmet causes the high rate of basilar skull fracture and the increased prevalence of severe injury associated with lateral impacts. The incorporation of an energy-absorbing earcup design is recommended to reduce the high rate of severe injuries associated with lateral impacts.