Dementia is one of the most common neurological disorders in the elderly. Aging is associated with a large increase in the prevalence and incidence of degenerative (Alzheimer's disease) and vascular dementia, leading to a devastating loss of independence. In view of increasing longevity of populations worldwide, prevention and treatment of dementia has turned into a major public health challenge. In the past decade, longitudinal studies have shown a close association between high blood pressure in middle age, cognitive decline and dementia, including Alzheimer's disease, in the late life. Pathophysiologically, a summation of cerebrovascular damage, white matter changes and pre-existing asymptomatic Alzheimer's brain lesions may lead to dementia, even when each type of lesion individually is not sufficiently severe to cause it. Longitudinal studies assessing the beneficial role of antihypertensive drugs on cognitive decline and dementia have produced promising results. There are few randomised placebo controlled studies, although some of these have produced positive results. Results of three recent meta-analyses are inconsistent, possibly due to methodological issues. Further long-term randomised trials, designed especially to assess a link between antihypertensive therapy and cognitive decline or dementia are therefore needed.