Nine patients with giant internal carotid artery (ICA) aneurysms (greater than 2.5 cm in diameter) were subjected to a combined extracranial-intracranial (EC-IC) bypass procedure and endovascular ICA occlusion during 1987 and 1988. The procedures were performed under one anesthetic. In all cases the collateral circulation had been judged insufficient on the basis of a strict preoperative testing protocol including: cerebral panangiography, electroencephalography, somatosensory potential recording, and cerebral blood flow monitoring during manual compression of the ICA in the neck. There were four intracavernous ICA aneurysms, four carotid-ophthalmic artery aneurysms, and one supraclinoid ICA aneurysm. All patients showed symptoms and signs of compression of the surrounding nervous structures. In the five cases of intradural lesions, the artery was occluded at the level of the aneurysm neck, so the ophthalmic artery had to be occluded. There was, nevertheless, no case of worsening of vision following surgery, and all nine patients showed significant improvement following the combined procedure. A combined EC-IC bypass procedure and endovascular ICA occlusion allows for immediate verification of the surgical results and appears to be a worthwhile method for treating giant intracranial aneurysms.