Aneurysms arising from the midbasilar trunk are not common, and surgical management of these aneurysms remains a difficult challenge to neurosurgeons because of its anatomic characteristics. The authors report on a patient with a ruptured aneurysm arising from the basilar artery at the origin of the anterior inferior cerebellar artery and projecting to the right and upward. The aneurysm was successfully treated by a subtemporal transpetrosal approach in an acute stage.