Fifty-two patients presenting with dementia were divided into a group in whom clinical features suggested an ischaemic basis (multi-infarct dementia) and a group in whom a primary degenerative process seemed more likely. Focal EEG changes and angiographic evidence of ischeamic areas and atheromatous disease of intracranial vessels were more common in the "ischaemic" than in the primary degenerative group. CBF was significantly reduced in the former but the regional pattern was equally distorted in the two groups. These findings strengthen the belief that the ischaemic score can identify those patients whose dementia is associated with vascular disease.