30 patients with megadolichobasilar artery, explored by angiography, are reported; 23 among them were first studied by computerized tomography and 4 by magnetic resonance. From the clinical point of view, 9 had transient ischemic attacks or definitive ischemia, 7 had subarachnoid or intracerebral hemorrhage, and 7 had deficits of the cranial nerves; in the other 7 cases the condition was incidentally discovered as isolated asymptomatic anomaly or with other unrelated lesions. Among the patients with ischemic symptoms, vertebrobasilar insufficiency and pontine infarction were the most common clinico-radiological findings. Among the patients with intracranial hemorrhage, four had associated aneurysm or arteriovenous malformations. CT and MR allow a correct diagnosis of this anomaly. MR seems to be superior to CT in delineating the relationship of the anomalous artery with the nervous structures, and the coexisting pathology.