It is clear that more incidental aneurysms will be encountered in the future. Approximately 5% or more of the population harbors these lesions, and advancing technology can be expected to demonstrate them with increasing regularity. Multiple aneurysms will also be found in at least 18% of patients with subarachnoid hemorrhage due to aneurysms. The best estimates suggest a rate of hemorrhage approximating 1%/year for incidental aneurysms and a 0.4 to 0.65% annual mortality rate for these lesions. It has also been shown that even small aneurysms may enlarge and bleed unpredictably with the passage of time. Surgery for incidental aneurysms of the anterior circulation can be accomplished without mortality and with an operative morbidity of 6.5%. Higher morbidity occurs in surgery for aneurysms in more difficult locations as well as larger aneurysms. The increased risk of bleeding from larger aneurysms, however, may justify the increased morbidity of surgery for these lesions. Surgery for incidental aneurysms can be recommended in healthy individuals whose anesthetic risk is acceptable and for aneurysms less than 1.5 cm in diameter arising from the middle cerebral and posterior communicating arteries. Advancing age alone is not a contraindication for surgery, nor is size greater than 1.5 cm in diameter; however, the latter factor increases the operative risk. Operations to clip aneurysms of the carotid bifurcation, carotid-ophthalmic, and anterior communicating arteries may also be recommended, but these aneurysms are more difficult to approach and surgery carries a higher morbidity. Larger aneurysms, greater than 1.5 cm in diameter, in patients over 60 years of age, and in less accessible locations may not benefit from operation because surgical morbidity for these lesions is high and with advancing age the lifetime risk of rupture has decreased. For incidental aneurysms of the posterior circulation there are insufficient data to make a recommendation regarding surgery, although it is anticipated that the counsel for anterior circulation aneurysms will apply. If operative mortality and morbidity are to be maintained at acceptable levels, incidental aneurysm surgery should be the province of the accomplished aneurysm surgeon who has available to him the most modern techniques and equipment. With the clipping of incidental aneurysms, hopefully the number of patients suffering from subarachnoid hemorrhage with its high morbidity and mortality rates can be further reduced.