Recent reports sustain the hypothesis of tight links between vascular and neurodegenerative diseases: associations between atherosclerosis lesions and Alzheimer's disease (AD), increased risk of AD for hypertensive subjects, decreased risk of dementia for elderly treated with hypotensive drugs, and a major impact of apolipoprotein E polymorphism, a protein of the lipid metabolism, on the occurrence of AD. All these results suggest that vascular determinants, both environmental and genetic, may predispose to or speed up dementia. As a major player of vascular homeostasis, the renin angiotensin system (RAS) proteins constitute an interesting source of candidate genes. Among these, the angiotensin I-converting enzyme gene (ACE), a central enzyme of the RAS, presents in its sequence a deletion (D)/insertion (I) polymorphism associated with variations of plasma ACE levels and with the risk of myocardial infarction. We explored the impact of this genetic polymorphism on the risk of cognitive impairment and of dementia in several epidemiological studies. Physiopathological hypotheses suggest a possible involvement of the RAS proteins in the occurrence and evolution of AD. Moreover, although inconsistent, several results of case-control studies tend to suggest that the ACE I/D genetic polymorphism may constitute a genetic susceptibility factor for dementia, reinforcing the hypothesis of a major implication of vascular risk factors in the occurrence of dementia.