The proposition that acceleration of the brain without direct impact to the head can result in brain injury is examined by reviewing a series of 414 road users who were fatally injured in the vicinity of Adelaide, South Australia. The series comprises 170 pedestrians, 10 pedal cyclists, 143 motorcyclists, and 91 vehicle occupants. In each case a member of the research team attended the autopsy to look for evidence of impact on the body, particularly to the head or face. The brain was examined by a neuropathologist and the type and pattern of injury was recorded. The circumstances of the crash were investigated, including an examination of the crash site and the vehicles involved and, where relevant, interviews with witnesses. In cases involving a motorcyclist the helmet worn was retrieved by the police and assigned to the research unit for examination. Particular attention was paid to the identification of objects causing injury to the head or face and also to objects impacted by a helmet. Brain injury was recorded as a cause of death in 55% of the 403 cases for which there was a clear classification of cause of death. Brain injury, at any level of severity, was identified by a neuropathologist in 86 percent of the 414 fatally injured road users in the sample, including 24 cases that were examined microscopically. There were no cases in which there was an injury to the brain in the absence of evidence of an impact to the head.