Vascular dementia is the second most common type of dementia in the elderly after the dementia of Alzheimer's disease. Six forms of vascular dementia have been described: multi-infarct dementia, lacunar dementia, Binswanger's subcortical encephalopathy, cerebral amyloid angiopathy, white-matter lesions associated with dementias, and single-infarct dementia. Each is described. Severe dementia is found in 5% of persons over age 65 and in 15% to 20% of persons over age 80 years. Alzheimer's disease accounts for 50% to 60% of cases of severe dementia and vascular dementia for 10% to 20%; 20% of the patients have both disorders. The incidence of vascular dementia, which seems to be declining, is about 7/1,000 persons/year. Hypertension is the most powerful risk factor for all vascular dementias. Vascular dementias can be accurately diagnosed by using clinical and mental state examinations, Diagnostic and Statistical Manual of Mental Disorders criteria, ischemic scores, and computed tomography or magnetic resonance imaging. The most successful treatment of vascular dementia is the prevention of cerebral infarcts. Study of the incidence of vascular dementias and their treatment will be included in the European Trial on Systolic Hypertension in the Elderly (SYST-EUR) of 3,000 elderly hypertensive patients.