OBJECTIVES: Aneurysms of the anterior cerebral circulation are usually found on the anterior communicating artery (ACoA) or peripheral portion (A2) of the anterior cerebral artery (ACA). Infrequently, they are found on proximal segment (A1) of the ACA. These are presented 0.88-2.1% of all intracranial aneurysm cases. There are few describing a series of patient with A1 aneurysms. In this report, we present our surgical experience of the 27 A1 aneurysms. MATERIAL AND METHODS: 27 patients with aneurysm of proximal segment of anterior cerebral artery were operated on between January 1983 and September 2004. Retrospective analysis of clinical characteristics, radiologic findings, operation method, clinical outcomes and complications were performed. RESULTS: 27 patients with aneurysm of proximal segment of anterior cerebral artery, male was 11 cases, female was 16 cases. Relatively, predominantly occurred in female. In preoperative Hunt-Hess grade (H-H grade) of the patient, H-H grade I was 10, gradeII in 13, grade III in 3, grade IV in 1 case. In CT findings, 23 cases presented only SAH, SAH and ICH in 4, accompanying hydrocephalus in 3 cases. In angiographics and surgical findings, according to aneurysm site, proximal type was 9 cases, middle type in 8, distal type in 10 cases, and compared with each clinical outcomes. In 9 patients, aneurysms was found in right side and 7 patients of these had favorable outcomes. In left side, 12 of 18 patients had favorable outcomes. Postoperative complication occurred in 8 cases, postoperative infarction in 3 case. vasospasm in 4 cases, hydrocephalus, meningitis in 4 cases. 5 patients had multiple aneurysms. In 2 cases of these, A1 aneurysm was ruptured. In 3 cases, other aneurysm was ruptured and A1 aneurysm was incidental finding. In total 27 patients, 19 patients had favorable outcomes and unfavorable outcomes in 8. CONCLUSION: Aneurysms of proximal segment (A1) of the anterior cerebral artery occur very infrequently and in this report, These are presented 3.9% (27 out of 680) in anterior cerebral artery aneurysms. 19 patients underwent direct surgery had good outcomes after the surgery. As causes of unfavorable outcomes, poor preoperative general condition, injury of perforating artery during operation and vasospasm. Comparison with other aneurysms, relative good outcomes can be obtained by direct surgery.