The purpose of this study is to determine whether three-dimensional computed tomography angiography (CTA) is superior to magnetic resonance angiography (MRA) in the evaluation of collateral circulation in patients with intracranial arterial occlusive disease. Conventional angiography was used as the standard reference. Collateral vessels were well visualized by CTA, but not by MRA, while conventional angiography revealed leptomeningeal collateral vessels that were filled in a retrograde fashion. CTA is superior to MRA for evaluating collateral vessels.