Based on the above review several general points can be highlighted: Head injuries are extremely common, affecting probably close to 2,000,000 people in this country each year. The most common are nonmissile, closed-head injuries, the majority of which occur in association with motor vehicle accidents. Virtually all studies of head injury suggest a peak incidence in the 15 to 24 years of age group. Coarse measures of outcome suggest that the very young and the elderly have poorer outcomes. Because of improved acute care, however, a large number of young, otherwise healthy patients are surviving head injuries with a variety of profound neuropsychiatric sequelae. Because of the mechanics of brain injury in acceleration-deceleration injuries, certain brain injury profiles are common including orbitofrontal, anterior and inferior temporal contusions, and diffuse axonal injury. The latter particularly affects the corpus callosum, superior cerebellar peduncle, basal ganglia, and periventricular white matter. The neuropsychiatric sequelae follow from the above injury profiles. Cognitive impairment is often diffuse with more prominent deficits in rate of information processing, attention, memory, cognitive flexibility, and problem solving. Prominent impulsivity, affective instability, and disinhibition are seen frequently, secondary to injury to frontal, temporal, and limbic areas. In association with the typical cognitive deficits, these sequelae characterize the frequently noted "personality changes" in TBI patients. In addition, these changes can exacerbate premorbid problems with impulse control. Marked difficulties with substance use, sexual expression, and aggression often result. The constellation of symptoms, which make up the postconcussive syndrome, are seen across the whole spectrum of brain injury severity. Even in so-called mild or minor head injury, these symptoms are likely to have an underlying neuropathologic, neurochemical, or neurophysiologic cause. Higher than expected rates of certain psychopathologic disorders occur in the TBI population, including psychotic syndromes and depressive syndromes. Manic syndromes also are associated with TBI; however, the incidence has not been established. Assessment and treatment of the neuropsychiatric sequelae is a complex and challenging process. The mixture of diffuse and focal injuries, the combination of cognitive, language, somatic, and behavioral difficulties do not fit easily into current diagnostic categories.