Accumulating research documents typical rates in the range of 85% of mild traumatic brain injury (MTBI) showing prompt, complete resolution with 15% suffering from persistent neurobehavioral impairments. Studies of neurobehavioral symptoms of MTBI have not separated these two populations, resulting in either inconclusive or contradictory conclusions concerning the relationship of MTBI with residual behavioral problems. This project studied 70 MTBI patients with persistent neurobehavioral problems at two time intervals post-injury to determine whether there are consistent neurobehavioral patterns considered to be sequelae of MTBI. A matched group of 40 normal subjects provided control data. While most behavioral problems showed improvement, 21% tended to show significant behavioral impairment compared to controls at 12 or more months post-injury. Neurochemical bases of neuronal degeneration may account for some of the behavioral deterioration following MTBI.