During the 14-year period up to September, 1975, 346 patients with a single anterior communicating artery aneurysm, including eight with unruptured aneurysms, were operated on by direct intracranial procedures. There was an early operative mortality of 5.5%. Follow-up studies, an average of 3 years 11 months after surgery, revealed that about 85% of the survivors, excluding those who could not be followed, had regained their working capacity, and that the late mortality and morbidity rates were 9.6% and 2.0%, respectively. The rationale for performing the intracranial operation and factors influencing postoperative results are discussed, with particular emphasis on the techniques for accurate treatment of aneurysms that help to prevent postoperative rebleeding and therefore give better overall surgical results.