The authors reported the cases of 23 patients with aneurysms measuring 2.5 cm or greater in diameter found during 7 years period in which we performed 596 operations for aneurysm of the 23 patients, 14 were treated by direct operation, 3 by internal carotid ligation with or without bypass surgery, 2 by trapping, 1 by wrapping and the other 3 by conservative therapy. The overall incidence of giant aneurysms was 3.9% but varied according to location; 9 cases were located on the internal carotid artery; 8 were on the anterior communicating artery; 5 were on the middle cerebral artery. 14 patients had hemorrhagic attacks, 7 had mass effects from the aneurysm, and 2 had ischemic events. Overall favorable outcome was 65% and the mortality was 13%. Based on the review of the literature, the appropriateness of surgery and surgical methods are discussed.