Bilateral vertebral angiography has been performed on 44 cases of vertebrobasilar ischaemia (VB I), excluding transient ischaemic attacks, and on 20 cases of carotid ischaemia with lesions of the vertebral artery (VA). Significant lesions (stenosis of more than 50% of the lumen and occlusion) of the VA were found in 72% of VB I and 70% of carotid ischaemia cases. In the VB I group, occlusions are as frequent as stenosis (17 occlusions and 15 stenosis); on the contrary, occlusions are half as frequent as stenosis in the carotid ischaemia group. Bilateral lesions are also more often discovered after VB I than after carotid ischaemia. Topographically, the lesions are mainly at the ostium and in the third portion of the VA. The possibility that vertebro-basilar strokes are related to significant lesions of the VA in its cervical part is emphasized. Haemodynamic disorder can explain infarcts related to bilateral lesions and some of those reported after unilateral lesions. Embolism may be suggested in cases of significant stenosis and of certain unilateral occlusions.