In order to reconstruct the blocked CSF pathway, we attempted to excise the Liliequist membrane in 22 patients with subarachnoid hemorrhage resulted from ruptured intracranial aneurysms. After clipping the aneurysmal neck, the Liliequist membrane was reached through the space between the optic nerve and the internal carotid artery within the same operative field. As a result, the incidence of postoperative ventricular dilatation was remarkably reduced in comparison with control cases without Liliequist membranotomy. The necessity for the shunt operation for post-SAH hydrocephalus was also reduced. On the other hand, the incidence of postoperative subdural effusion increased in the group with Liliequist membranotomy. This suggests that the blockage of the arachnoid villi is probably the cause of disturbances in CSF absorption in some cases following subarachnoid hemorrhage. In such cases, the Liliequist membranotomy may be ineffective in restoring CSF circulation following subarachnoid hemorrhage.