We have studied a patient with tight narrowing of both internal carotid arteries (ICAs) due to giant-cell arteritis. Although the brain supply through the internal and external carotid arteries pathways was totally inefficient, the patient suffered a progressive extensive infarction limited to the vertebrobasilar/posterior cerebral arteries area, except small lesions in the internal capsules. Both vertebral arteries were patent, although a fresh clot partially filled one of them. Without evidence for distal embolization, intracranial involvement by the arteritis, or generalized hypotension, we suggest that our patient suffered an intracranial steal phenomenon from the vertebrobasilar system towards the carotid circulation.