Mild traumatic brain injury (MTBI) accounts for approximately 80% of the estimated 373000 traumatic brain injuries that occur annually in the United States. MTBI typically occurs in males 15 to 24 years of age, and postconcussional sequelae may impede physical, emotional, social, marital, vocational, and avocational functioning. Usually the severity of the initial neurologic injury is defined according to the Glasgow Coma Score, the presence and duration of amnesia (retrograde and anterograde), and the alteration of loss of consciousness and its duration. MTBI is a traumatically induced physiological disruption of cerebral function manifested by at least one of the following: loss of consciousness no longer than 20 minutes; any loss of memory; any alteration in mental status at the time of the accident; physical symptoms that potentially are related to the brain; and development of posttraumatic cognitive deficits not accounted for by emotional factors. When a patient presents with multisystem trauma, impairments may involve several parts of the body, including the nervous system. Individual impairments of other systems should be calculated separately and their whole person values combined using the Combined Values Chart in AMA Guides to the Evaluation of Permanent Impairment. At present, no ideal system can rate impairment following MTBI, and physicians must thoroughly understand both the underlying disease process and the associated injuries.