In previous reports from this hospital no attempt has been made to evaluate the effects on patients of various methods used in treating intracranial aneurysms. Statistics including the entire group of 163 verified aneurysms are no longer of value in determining the effects of surgical therapy. The present report concerns only the cases in which nonfistulous aneurysms, localized by angiography, were attacked in a definitive manner. MATERIAL This series (Table 1) includes 69 cases, in which 51 patients were treated, with a mortality rate of 21.5%, and 18 were untreated, with a mortality rate of 61%. The total fatality rate was 32%. Subarachnoid Hemorrhage and Time of Operation Aneurysms had ruptured, producing subarachnoid hemorrhage in 43 of the 51 patients treated and in 15 of the 18 untreated. As others also have reported, the risk of operation in these cases is greatest in the first week after hemorrhage. Of seven