Mild head injury classification. Inconsistencies across studies concerning outcome after mild head injury may reflect differences in the diagnostic criteria used for selection of patients. Consequently, we compared the neurobehavioral outcome in three groups of consecutively hospitalized patients (aged 16 to 50 years) who sustained a closed head injury (CHI) and had a Glasgow Coma Scale (GCS) score in the 9 to 15 range. These groups included patients with uncomplicated CHI with mild impairment of consciousness as reflected by a GCS score in the 13 to 15 range (n = 78), patients with initially mild impairment of consciousness complicated by brain lesion or depressed skull fracture (n = 77), and patients with moderate CHI (n = 60). Tests of memory, information processing, and verbal fluency were administered within 1 to 3 months after injury, and the Glasgow Outcome Scale was completed at 6 months. Neurobehavioral functioning was impaired in the groups with complicated mild CHI and moderate CHI as compared to the group with uncomplicated mild CHI. Although moderate CHI produced longer durations of impaired consciousness and posttraumatic amnesia than complicated mild head injury, patients in these groups did not differ in neurobehavioral performance. Global outcome at 6 months was better in the patients with mild CHI than in patients with complicated mild and moderate injuries. Analysis of the various complications of mild CHI revealed that the presence of an intracranial lesion was related to more severe neurobehavioral sequelae than injuries complicated by a depressed fracture. 