We have divided head injury into three categories based on the Glasgow Coma Scale (GCS) (severe, 3-8; moderate, 9-12; and minor, 13-15). In a previous report, we described significant disability after minor head injury. The present report describes 199 patients with moderate head injury, 159 of whom underwent follow-up examinations at 3 months. In contrast to patients with minor head injury, half as many were students (17%) and twice as many were intoxicated (53%). Seventy-five patients were studied with computed tomographic (CT) scanning; 30% of the scans were negative and 31% showed a space-occupying mass. As reported by Gennarelli et al. in patients with severe head injuries, those with moderate head injury and subdural hematoma had a very poor outcome: 65% died or were severely disabled and none made a good recovery as measured by the Glasgow Outcome Scale. At 3 months, 38% of the moderate head injury patients had made a good recovery compared with 75% of the minor head injury patients. Within the good recovery category, however, there was much disability (headache, 93%; memory difficulties, 90%; difficulties with activities of daily living, 87%), and only 7% of the patients were asymptomatic. The Halstead-Reitan Neuropsychological Battery in an unselected subset (n = 32) showed significant deficits on all test measures. Sixty-six per cent of the patients previously employed had not returned to work, compared to 33% of the minor head injury patients. The major predictors of unemployment after minor head injury were premorbid characteristics (age, education, and socio-economic status). In contrast, all predictors in moderate head injury were measures of the severity of injury (length of coma, CT diagnosis, GCS on discharge). We conclude that: (a) moderate head injury, not described previously in the literature, results in mortality and substantial morbidity intermediate between those of severe and minor head injury; (b) unlike minor head injury, the principal predictors of outcome after moderate head injury are measures of the severity of injury; and (c) more attention should be directed to patients with moderate head injury than to those with the most severe injuries, in whom brain damage is probably irreversible and all forms of management have demonstrated little success.