BACKGROUND: It is well known that the global population is aging and that those over the age of 80 are the fastest growing part of this expansion. Also known is that prevalence of hypertension and cognitive decline both increase with increasing age. METHOD: The Hypertension in the Very Elderly Trial (HYVET) was a double blind placebo-controlled trial of antihypertensive treatment (indapamide SR 1.5 mg +/- perindopril 2-4 mg) and recruited only those hypertensives who were aged 80 or over and were without a diagnosis of dementia at baseline. Systolic blood pressure had to be in the range 160-199 mmHg and diastolic pressure <110 mmHg. Cognitive function was assessed at baseline using the Mini-mental State Examination prior to randomization into the trial. Also collected at baseline was information relating to sociodemographic, clinical, cardiovascular and biochemical factors which may impact upon cognitive function. This paper reports on the baseline cognitive function data from the HYVET trial and its relationship to these factors. RESULTS: The mean age of the 3763 HYVET participants who had full cognitive function data at baseline was 83.6 years; 60 percent were female. The median MMSE score at baseline was 26 and, in multivariate analyses, higher at younger age, with male gender, higher educational level, having higher creatinine, higher total cholesterol and lower high-density lipoprotein cholesterol. CONCLUSIONS: This is the first such study to examine a large number of very elderly hypertensives and it shows some similar patterns to those seen in younger elderly groups.