Although considerable gross damage to the brain may be found, on surgical intervention or at autopsy, in many head injuries, it is often slight, and usually insufficient to explain either the patient's death or even his neurological symptoms. Consequently, several workers (1, 2) have postulated the existence of a diffuse lesion involving both the nerve cells and their pathways throughout the brain. Indeed, microscopic examination may reveal widespread damage to the white matter following a head injury which does not necessarily produce hemorrhage, contusion or laceration (3, 4). The degeneration is thought to be due to the stretching and tearing of nerve fibers at the moment of the accident. Patients showing this microscopic change, however, usually have been severely incapacitated and have survived for a long time following the injury. It seems possible that lesser degrees of white matter damage may occur in all patients with head injury, but the frequency is difficult to estimate as too few acute head injuries have been investigated histologically. This paper describes the neuropathological changes in the white matter in 40 consecutive head injuries.