Seemingly mild head injuries frequently result in persisting postconcussive syndromes. The etiology of these symptoms is often controversial. Neuropsychological, neurophysiological, and neuropathological evidence that brain damage can occur in the absence of gross neurological deficits after mild injuries is reviewed. Direct impact to the head is not required to cause brain injury. Understandably, psychological factors also play a role in post-head-injury disability, but the effect of compensation claims and preinjury psychopathology is often secondary to organic factors. Persons over age 40 or with a history of previous head injury are more vulnerable to protracted symptomatology.