Closed head injuries are common, affecting approximately 2 million people annually in the United States. The majority of these are "mild" in the sense of not being associated with prolonged unconsciousness, intracranial bleeding, skull fracture, or protracted periods of confusion. Yet a proportion of such "mild" injuries are accompanied by persisting cognitive, vegetative, and affective-behavioral sequelae, some of which affect day-to-day life. We argue that there is sufficient research to indicate that postconcussional symptoms occur and that they tend to have a predictable configuration. It is necessary to recognize the existence of "Postconcussional Disorder" in our nosology in order to provide more prompt diagnosis and management and to facilitate scholarly communication and research regarding this important neurobehavioral disorder.