Following the definition of. the syndrome of subarachnoid hemorrhage by Symonds1in 1923, its recognition has presented little difficulty. Excellent descriptions of the syndrome and summaries of the literature have been presented by Strauss, Globus and Ginsburg,2Sands3and Dandy.4 Subarachnoid hemorrhage is responsible for 2 per cent of sudden deaths.5It comprises 7 per cent of all cerebral vascular disease and approximates in frequency parenchymatous cerebral hemorrhage (8 per cent).6The most common cause of subarachnoid hemorrhage is rupture of intracranial arterial aneurysms. Among others the studies of Bremer,7Forbus,8McDonald and Korb,9Richardson and Hyland10and Magee11have contributed much to our knowledge of the formation, occurrence and natural history of intracranial arterial aneurysms and their role in the production of subarachnoid hemorrhage. Dandy4has recently reported his pioneer work in the surgical treatment of intracranial