To study the relationship between the severity of impact to the head and the severity and distribution of injury to the brain in fatally injured pedestrians, events in vehicle-pedestrian collisions were reconstructed to determine the peak linear and angular acceleration sustained by the pedestrians' heads. The nature and distribution of injuries to the brain were determined by neuropathologic examination of coronal sections of the brain. Study of 13 cases with occipital impacts and 18 with lateral impacts showed that the brain appeared to be more susceptible to injury from lateral impacts. The frontal and temporal regions appeared to be more susceptible to injury at low accelerations in occipital impacts, providing an explanation for "coup" and "contrecoup" injuries. For occipital impacts, a positive relationship was found between linear acceleration and the extent of injury to the brain, suggesting that there was a threshold for observable and concussive brain injury at about 1500 m/s2 peak linear acceleration. These findings are important for the development of measures for preventing brain injuries.