A 6-year retrospective analysis of incidental intracranial aneurysm surgery was conducted at 12 medical centers (1975-1981). The surgical facilities and techniques were comparable at the institutions surveyed. From a total of 1671 aneurysms operated upon, 119 in 107 patients were unruptured and were discovered incidentally. Among these 107 patients, there was no operative mortality. Operative morbidity occurred in 7 cases (6.5%). Surgical treatment of large aneurysms in less accessible locations incurred the greatest operative morbidity. Presenting symptoms of cerebral ischemia seemed to be associated with increased operative morbidity, whereas repair of aneurysms incidental to other ruptured aneurysms had a uniformly low morbidity. These surgical results compare favorably with the risks of hemorrhage from unruptured intracranial aneurysms as defined by recent reports. The low morbidity without mortality supports a recommendation for surgical management of incidental aneurysms in the anterior circulation at centers equipped for modern aneurysm surgery.