Seventy consecutive cases of internal carotid artery aneurysm were operated on utilizing the surgical microscope. There were three deaths (4.3% mortality), one of which occurred in a deeply comatose apneic patient. Fifty-nine patients (84%) had excellent results. Four (6%) had postoperative morbidity directly related to their operation; three of them were operated on within 2 weeks after subarachnoid hemmorrhage and had neurological deficits attributed to cerebrovascular spasm. The low morbidity and mortality rates are partially related to patient selection but also significantly influenced by improved surgical techniques made possible by the microscope and microsurgical instrumentation. It is the authors' opinion that microsurgery should be standard procedure for craniotomy for intracranial aneurysm. It is suggested that future reported series of aneurysm therapy, regardless of the method of treatment employed, should be compared with the anticipated natural history.