Background: Although it is well recognized that the diagnosis of hypertension should be based on blood pressure (BP) measurements taken on several occasions, notably to account for a transient elevation of BP on the first readings, the prevalence of hypertension in populations has often relied on measurements at a single visit. Objective: To identify an efficient strategy for assessing reliably the prevalence of hypertension in the population with regards to the number of BP readings required. Design: Population-based survey of BP and follow-up information. Setting and participants: All residents aged 25-64 years in an area of Dar es Salaam (Tanzania). Main outcome measures: Three BP readings at four successive visits in all participants with high BP (n = 653) and in 662 participants without high BP, measured with an automated BP device. Results: BP decreased substantially from the first to third readings at each of the four visits. BP decreased substantially between the first two visits but only a little between the next visits. Consequently, the prevalence of high BP based on the third reading - or the average of the second and third readings - at the second visit was not largely different compared to estimates based on readings at the fourth visit. BP decreased similarly when the first three visits were separated by 3-day or 14-day intervals. Conclusions: Taking triplicate readings on two visits, possibly separated by just a few days, could be a minimal strategy for assessing adequately the mean BP and the prevalence of hypertension at the population level. A sound strategy is important for assessing reliably the burden of hypertension in populations.