The prevalence of poststroke dementia (PSD) varies largely according to the composition of cohorts, setting, and delay after stroke. The cognitive syndrome of vascular dementia (VaD) is characterized by: memory deficit, dysexecutive syndrome, slowed information processing, and mood and personality changes. Cortical VaD relates to large vessel disease, cardiac emboli, and hypoperfusion. It prominently shows cortical and corticosubcortical arterial territorial and distal field infarcts. The occurrence of dementia depends on two factors: the total volume of brain loss because of infarcts and hemorrhages, and the location of these lesions. Many instances of dementia occurring in stroke patients are probably the consequence of the cumulative effect of the cerebrovascular lesions, Alzheimer pathology, and white matter changes. Patients with dementia after stroke are significantly less often treated with aspirin or warfarin than nondemented patients. Trials of secondary prevention of stroke usually exclude patients with obvious dementia.