A cause and effect relationship between arterial hypertension and decline of cognitive function has long been suspected. In middle-age subjects indeed, an abnormally high blood pressure is a risk factor for the long-term development of dementia. Presently, it seems crucial to treat hypertensive patients in order to better protect them against cognitive decline. However, in the elderly patients the risk of mental deterioration may also be enhanced when diastolic pressure becomes too low, for example below 70 mmHg. Further studies are required to better define the antihypertensive drug regimen and target blood pressure which would be optimal for the prevention of cerebral small vessel disease.