Two cases of aneurysms with basilar artery fenestration are presented. A 45 year-old lady had a saccular aneurysm associated with a fenestrated basilar artery. The fenestration was located in the proximal third of the basilar artery. The aneurysm arose from the proximal end of the fenestration, projecting antero-inferiorly. Via a left retromastoid craniectomy, the aneurysm was successfully obliterated through the space between the eighth cranial nerve and the lower cranial nerve complexes. Postoperative deficit in the lower cranial nerves was minimal and transient. The other patient, a 63 year-old lady, had multiple aneurysms arising from the anterior circulation associated with a basilar artery fenestration. These aneurysms were clipped uneventfully. Surgical approach to an aneurysm arising from the basilar artery fenestration is discussed with other related literature. Full study of posterior circulation with multiple projection is mandatory to detect basilar artery fenestration, and the possible presence of saccular aneurysm at the site of the anomaly.