Because of the aging population, the frequency of dementia will dramatically increase in the coming years. Prevention of cognitive disorders and dementia has become a major public health challenge. High blood pressure is a major risk factor for cerebrovascular diseases and is also correlated closely with cognitive decline and dementia. Several epidemiologic studies have found that cognitive functions are often inversely proportional to blood pressure values measured 15 or 20 years previously. Moreover, the use of antihypertensive drugs has been shown to help prevent cognitive decline, opening the way to the prevention of dementia (vascular or Alzheimer's type). These results indicate that incidence of dementia should constitute a major outcome of future trials comparing different classes of antihypertensive drugs.