Hypertension and dementia commonly co-exist in older people, yet guidance is lacking on how to manage these co-existing conditions. The aim of this systematic review was to assess the evidence for the treatment of hypertension in older people with dementia. Medline, EMBASE, Cochrane Library and the national research register archives were searched. Inclusion criteria were: randomised controlled trial of hypertension treatment, included participants aged 65+ years, participants had a diagnosis of dementia (global cognitive decline for at least 6 months affecting daily function), and the study assessed cognitive outcomes using validated tools. Dementia prevention studies and poor quality studies were excluded. The initial search revealed 1178 papers of potential interest, of which 24 were selected for review and six met the full inclusion criteria. Trials included people with mild-to-moderate but not severe dementia; exclusion criteria for the trials were extensive. Four trials were placebo-controlled RCTs; the remaining two compared different antihypertensives. All trials reported MMSE scores at baseline and follow-up; four reported blood pressure changes at follow-up; and only three reported cardiovascular morbidity or mortality at follow-up. Only one of four placebo-controlled studies showed evidence of blood pressure reduction, but no clear evidence for benefit (or harm) from antihypertensives on cognition, physical function or other cardiovascular outcomes. We found no evidence to confirm or refute the hypothesis that treatment of hypertension in people with dementia leads to overall health benefit.