Significant associations have been reported between cognitive decline, dementia and measures of cardiovascular and cerebrovascular disease. Such findings raise important possibilities for prevention of dementia through reducing the burden of vascular pathology. However, given the long prodromal periods for both clinical vascular disease and dementia, the most fruitful way forward may lie in investigating the effects of risk factors for vascular disease, rather than clinical vascular disease itself. Hypertension has received considerable attention in this respect although it is only recently, thanks to findings from prospective population-based research, that the complex interrelationship between blood pressure levels and cognitive decline has begun to be clarified.