There are limited, reliable data on the prevalence of hypertension in East African populations. The aim of this study was to document the prevalence of hypertension in the rural Hai district of Tanzania. All consenting individuals aged 70 years and over who were living in 12 randomly-selected villages in the district underwent three consecutive sitting blood pressure (BP) measurements. An average of the last two measurements was taken. Prior diagnosis of, and treatment for, hypertension was recorded. Of the 2223 subjects, 1553 (69.9%, 95% CI 68.0-71.8) had hypertension (BP ≥140/90). Of those with hypertension 733 (47.2%) had isolated systolic hypertension. Only 586 (37.7%) hypertensives had been previously diagnosed, 94 (6.1%) were currently treated and 14 (0.9%) were adequately controlled. This is the first large-scale prevalence study of hypertension in the elderly in sub-Saharan Africa (SSA). Our results approximate to a 'rule of sixths'; 2/6 of hypertensives were previously detected, 1/6 of those previously detected were on treatment and 1/6 of those on treatment were adequately controlled. Hypertension is a large problem in the elderly population in SSA, and there are a growing number of elderly who are at risk of hypertensive sequelae owing to lack of detection and treatment.