Two thirds of 56 patients suffering spontaneous cerebellar hemorrhage were responsive on admission. The diagnosis was made solely on clinical bases in the majority of cases. Timing and rate of clinical deterioration were unpredictable in individual cases, especially in the initial hours and days after onset. Fifty percent of patients became comatose by 24 hours and 75% within one week after onset. The results of surgical decompression were strongly influenced by preoperative mental status: 17% mortality for responsive and 75% for unresponsive patients. However, nine patientssurvivedwithout undergoing surgical decompression. Our results suggest that substantial improvement in the overall mortality could be made by immediate craniectomy and evacuation of hematoma in all patients encountered within 48 hours of onset, and in most within a week after onset.