Treatment of giant aneurysms of the basilar artery remains difficult and controversial. Especially, surgical treatment of the basilar trunk aneurysm have a potential morbidity or mortality due to its anatomical environment and the complicated surgical exposure. A 32-year-old female presented with an unruptured, giant basilar trunk aneurysm manifesting as brainstem compression signs and cranial nerve dysfunction. Cerebral angiography disclosed a giant aneurysm with a wide neck and an intra-aneurysmal thrombus arising from the mid-basilar artery. Aneurysm was embolized with Guglielmi detachable coils; and complete occlusion of the aneurysm was obtained.