This study evaluated the incidence and outcome of serious brain injury from traffic-related causes in 695 patients admitted to the Department of Neurosurgery at Karolinska Hospital during 1981-1992. A total of 37.3% of patients were car occupants, 28.1% pedestrians, 12.9% bicyclists, 12.2% car-bicycle/car-moped and 9.5% motorcycle riders. The dominating injury was brain contusion (61.6%) verified with computerized tomography. The level of consciousness was evaluated by the Glasgow Coma Scale (GCS) and outcome by the Glasgow Outcome Scale (GOS) at discharge and 6-36 months thereafter. The final outcome was 67.5% good recovery (GOS 4-5), 11.5% severely disabled (GOS 2-3) and 21.0% GOS 1 or brain dead. Patients with GOS < 4 (32.5%) were severely disabled and motivate priorities for injury prevention. Car occupants represent 40.7% of the total, followed by pedestrians at 33.6% and bicyclists at 18.2%. Much remains to be done in the primary prevention of disabling brain injury to car occupants and pedestrians. In order to achieve a more-effective primary prevention, future research should be directed toward biomechanical aspects of brain contusion as a dominating brain injury.