Sixty patients with acute subdural hematoma were treated at Tokyo Metropolitan Hiroo Hospital between 1981 and 1989. The overall mortality was 55% and the functional recovery rate 30%. Thirteen (93%) of 14 patients with a Glasgow Coma Scale (GCS) score of 3 died, while all eight patients with a GCS score of 7 or more achieved functional recovery. The mortality of patients with GCS scores of 4-6 ranged from 45 to 67%. Patients with GCS scores of 4-6 over 65 years old had a mortality of 82%, compared to 50% mortality for those aged 19-40 years. The mortality for patients with GCS scores of 4-6 operated on within 4 hours of injury was 62% in contrast to 33% for those operated on from 4 to 10 hours. Patients with GCS scores of 4-6 who underwent craniotomy with evacuation of the hematoma achieved significantly better recovery than those treated by burr holes. Four patients with GCS scores of 4-6 died in spite of decompressive craniectomy or craniotomy with duroplasty. The mortality is only influenced by age and type of surgical intervention among patients with GCS scores of 4-6. Shorter time from injury to surgical evacuation does not affect mortality within 10 hours of injury.