Male drivers sustained relatively more serious motorcycle collision injuries than did male passengers, female drivers, or female passengers. For male drivers, severity of injury was related to age. The relative frequency of serious head injury was highest for drivers not wearing helmets who were involved in collisions at low or high speeds. Severity of injury was related to speed at the time of collision but not in all types of collisions. Factors associated with the incidence of collisions were not identical to those related to the severity of the injury sustained.