The prevalence and incidence of dementias are expected to increase in the future. Accordingly, the identification of causes of dementia and of possible risk factors is very important. A large body of evidence has shown that hypertension is a risk factor for vascular dementia. Recently, it has been demonstrated that hypertension could affect the course of Alzheimer disease. A strong relationship between hypertension and cognitive decline (CD) or dementia has been reported by several observational studies, especially in untreated subjects. The risk increases with increasing blood pressure (BP). However, this relationship is not linear, since BP may decrease to normal or low levels before dementia becomes clinically manifest. There may also be an association between BP variability in hypertensive patients and impaired cognition. Recent studies, using the 24-hour non-invasive monitoring, have shown that both short-term and longterm BP variability are associated to CD. This variability may reflect central nervous system dysregulation or occult injury to prefrontal autonomic centers. Trials with antihypertensive drugs focusing on CD and dementia have shown that active treatment may be beneficial, although the optimal BP levels have not yet defined. Future studies, comparing the different effect of antihypertensive drugs are expected to further clarify this topic.