High blood pressure is associated with an increased risk of vascular dementia as a result of ischemic stroke and other cerebrovascular events or lesions. However, there is insufficient epidemiologic evidence indicating that blood pressure is involved in the etiology of Alzheimer's disease. Clinical studies suggest that episodes of hypotension may cause cerebral hypoperfusion and play a role in the development of dementia. Lowering of blood pressure in dementia, especially Alzheimer's disease, may be due to the dementia process itself or to the characteristics of the disease. Recent large clinical trials have shown that antihypertensive drugs may not significantly affect cognitive performance, but no data are available regarding their potential effects in decreasing the risk of dementia by lowering the incidence of cerebrovascular events. Some data suggest that the blood pressure-dementia relationship may be age-dependent.