Hypertension is a risk factor for stroke, ischemic white-matter lesions, cardiovascular disorders, and vascular dementia. This risk increases with increasing blood pressure. Several studies report that high blood pressure precedes Alzheimer's disease (AD) by decades, but blood pressure decreases the years before dementia onset and is lower in individuals with AD than in controls. High blood pressure has also been related to the neuropathological manifestations of AD. The exact mechanism behind these associations is not clear. Hypertension may cause cerebrovascular disease that may increase the likelihood that individuals with AD encephalopathy will express a dementia syndrome, this may accelerate the AD process, subclinical AD may lead to increased blood pressure, and similar biological mechanisms may be involved in the pathogenesis of both disorders. Hypertension is a common disorder and often untreated. Even if hypertension results only in a moderately increased risk of AD, or overall dementia, better treatment of hypertension may have an immense effect on the total number of individuals with dementia.