Occlusion of the anterior cerebral artery is a rare condition. A review of CT scans from 413 patients with ischemic infarction confirmed this low relative incidence: only 3% of CT scans evidencing infarction involved the territory of the anterior cerebral artery. Four major mechanisms of anterior cerebral artery occlusion have been identified in this series: Emboli in unusual hemodynamic circumstances such as patients presumed to have increased flow through the anterior communicating artery because of unilateral internal carotid artery occlusion. Propagation of thrombotic material from an occluded internal artery into the intracranial branches. Spasm, emboli or propagating thrombosis associated with anterior communicating aneurysm.