We retrospectively evaluated efficacy and risk of external ventricular drainage which was performed in early management of high grade subarachnoid hemorrhage. Acute ventricular drainage was performed on 36.6% of 93 patients with grade V subarachnoid hemorrhage. The percentage of patients whose GCS improved following ventricular drainage were 14.3% from GCS 3, 61.5% from GCS 4, 42.9% from GCS 5 and 42.9% from GCS 6. The occurrence rate of rebleeding was approximately three-fold higher in patients who underwent ventricular drainage than in patients who did not. Aneurysmal surgery performed after ventricular drainage, compared with acute aneurysmal surgery, resulted in the smaller percentage of patients who became persistently vegetative and in the larger percentage of patients who became severely disabled, while it did not change the percentage of patients who resulted in favorable outcome and death. These results of retrospective study suggested that ventricular drainage performed on grade V subarachnoid hemorrhage increased the risk of rebleeding and did not increase the percentage of patients who resulted in favorable outcome although it reduced the percentage of patients who resulted in persistent vegetative state.