In this article, we look at the literature concerning the relationship between blood pressure and cognitive function. If untreated, hypertension leads to stroke or cerebral infarction, and may therefore increase the risk of dementia or cognitive impairment. Patients with hypertension perform less well in some, but not all, cognitive tasks compared with normotensive individuals, even in the absence of overt stroke. The mechanisms underlying hypertension-related cognitive changes are complex and are not yet fully understood. Antihypertensive drug therapy may prevent cognitive decline, but no longitudinal studies have been performed to verify this in the general population. The relationship between blood pressure and cognition may be more complicated in the very old than in other age groups.