The importance of lowering blood pressure (BP) in hypertensive subjects is well known but the relationship between hypertension and cognitive function is controversial. This article reviews the role of hypertension in the aetiology of cognitive impairment and the relationships between BP, cerebral perfusion and cognition. It also summarizes findings of studies addressing the effect of antihypertensive therapy and cognition. An electronic database search of MEDLINE, EMBASE and the Cochrane Library and extensive manual searching of articles were conducted to identify studies that have used objective measurements of BP and neuropsychological tests to investigate the relationship among hypertension, cognitive function and/or antihypertensive treatment. In total, 28 cross-sectional studies, 22 longitudinal studies and 8 randomized placebo-controlled trials met the inclusion criteria. Cross-sectional studies showed mixed relationships between higher BP and cognition, with many studies showing no correlation or even J- or U-shaped associations. The majority of longitudinal studies demonstrated elevated BP to be associated with cognitive decline. Randomized studies demonstrated heterogeneous and, sometimes conflicting, effects of BP lowering on cognitive function. Suggested reasons for this heterogeneity include multiple mechanisms by which hypertension affects the brain, the variety of cognitive instruments used for assessment and differences in antihypertensive treatments. Although lowering the BP is beneficial in most patients with vascular risk factors, the effects of BP reduction on cognition remain unclear. Given the predicted upswing in people with cognitive impairments, the time is right for randomized clinical trials with specific cognitive end points to examine the relationship between cognitive function and hypertension and guide practice.