Prevention of dementia: Life expectancy still increases linearly, and the elderly part of the European population grows rapidly in relation to the young. Dementia, however, grows even more rapidly, because it increases exponentially after age 65; it will become a great burden if nothing is done. The discussion so far is concentrated on treatment, whereas prevention is neglected. The therapy of dementia, however, has limited effect. Contrary to a widespread opinion prevention is possible. Genetic factors alone dominate the fate of cognition only in about 3 % of the cases. Besides age, lifestyle and the vascular risk factors exercise a great influence. High blood pressure carries a fourfold risk, diabetes more than doubles the risk both of the vascular and of the Alzheimer type; combined even more. Especially cerebral microangiopathy is strongly associated with Alzheimer's dementia, it triggers the vicious circle which leads to amyloid deposition. The importance of the circulation is underestimated, because most of the microvascular cerebral lesions are not perceived by the patient. All the risk factors for Alzheimer's disease after age 65 are also vascular risk factors especially for microangiopathy: Apo-E4, oestrogen deficiency, insulin resistance, diabetes, arterial hypertension, high cholesterol, old age and increased plasma homocystin which is often caused by alcohol consumption even in moderate doses. A healthy life style with daily outdoor activity and a Mediterranean diet not only reduces the risk of dementia, but also of coronary death and cancer. Cognitively stimulating activity protects even more than physical activity against dementia; the basis for this is acquired in youth by education. Therapy with statins is advisable if atherosclerosis cannot be reasonably counteracted by physical activity and diet.