Surgical results in 82 cases with aneurysm (61 ruptured and 21 unruptured) of the bifurcation of the basilar artery were analyzed and the causes of unfavorable outcome and its measures were discussed. Operation was performed in grade I, II, III, or IV of the Hunt and Kosnik's classification for the patients with ruptured aneurysm. Both in ruptured and unruptured cases, patient's age was not considered. As it turned out, 10 elderly (70 years old or older) cases (8 ruptured and 2 unruptured) were included in this study. Unilateral pterional approach was adopted for all but one case, and temporary clip and/or division of the hypoplastic posterior communicating artery was actively used. Surgery was completed with clipping of the aneurysm in all but six cases and overall surgical result consists of 70% of favorable outcomes. The main causes of unfavorable outcome were surgical procedures and primary brain damage due to subarachnoid hemorrhage. And the factors influenced to increase surgical technical damage to the brain were the patient's age, size of the aneurysm, and/or height of the neck from biclinoids line. The outcome of the higher grade (grade III or IV) in elderly cases was miserable, whereas it was not different from anterior circulation aneurysms in younger cases. From the result we concluded that the surgical indication for elderly cases should be limited in cases with lower grade (grade I or II) without large and/or high-positioned aneurysm. To obtain further improvement of the surgical result in younger cases, additional surgical techniques have to be considered to avoid the injury of perforating arteries from P1 and to reduce the pressure of the brain retraction which are the most important hazards for aneurysm surgery in this area.