Of 366 consecutive patients with severe head injury, treated and managed by a uniform protocol, 61 (17%) were admitted with signs of severe brain-stem dysfunction. Forty-three of the 61 patients (70%) had surgical mass lesions and 30% had diffuse brain damage. Twelve of the 61 patients (20%) survived, but only six patients made a good to moderately disabled recovery. All six of these patients had a traumatic acute subdural hematoma (SDH). The records of the 20 comatose patients with an acute SDH and severe brain-stem dysfunction were reviewed to discover which factors contributed to functional recovery. The average survivor was operated on within 2 1/2 hours after injury and the nonsurvivors within 4 1/2 hours. Prompt surgical intervention and prudent control of postoperative intracranial pressure were major factors in preventing permanent brain-stem damage, with a significance of p less than 0.05 and p less than 0.02, respectively. Measurement of multimodality evoked potentials in the early postoperative period correctly distinguished between reversible and irreversible brain-stem dysfunction in six of the seven patients.