Spin-echo sequences allow an identification of the basal brain vessels because of their typical signal void. The increasing use of MRI also in clarification of cerebrovascular disease requires a good knowledge of intracranial flow alterations. We saw characteristic signal pattern in the carotid siphon in 22 prospective examined patients with occlusion of the internal carotid artery confirmed by ultrasound. The lower siphon showed a loss of flow void and a brain isointense signal. The signal in the upper siphon was identical or showed a flow void with significant calibre reduction, probably because of collateral filling. This diagnostic potential of MRI is a remarkable advantage in comparison to CT and should be routinely considered in patients with cerebrovascular disease.