Case-control transversal studies have suggested the existence of an association between low blood pressure and Alzheimer's disease, although there is some doubt on the cause to effect relationship. A drop in blood pressure preceding the onset of dementia has been evoked but never confirmed. Longitudinal studies, with long term follow-up on the existence of hypertension during middle-age, have demonstrated a significant increase in the risk of developing Alzheimer's disease in cohorts of hypertensive patients compared to normotensive subjects. The potential benefit of preventive treatment with antihypertensive drugs in decreasing the risk of Alzheimer's disease has not been confirmed in clinical trials. The hypothesis of the formation of a cerebrovascular disease that would combine with the neuropathological lesions has been evoked, raising doubts on the diagnostic criteria used to define Alzheimer's disease. The novel concept that vascular risk factors could directly induce the formation of neuropathological lesions is interesting but warrants confirmation.