To estimate the effectiveness and cost-effectiveness of blood pressure-lowering treatment over a lifetime. Markov decision analysis model comparing treatment and non-treatment of hypertension. Hypothetical cohorts for 20 different strata of sex, age (30-79 years, in 10-year age bands), and cardiovascular risk (low and high risk). Life expectancy, and incremental cost : effectiveness ratios for treatment and non-treatment strategies. In terms of life expectancy, blood pressure treatment increased life expectancy in all age, sex, and risk strata, by between 1.6 and 10.3%, compared with a policy of non-treatment. In terms of cost-effectiveness, treatment was more effective, but also cost more than non-treatment for all age, sex, and risk strata except the oldest high-risk men and women. Incremental cost per quality-adjusted life year (QALY) among low-risk groups ranged from pound 1030 to pound 3304. Cost-effectiveness results for low-risk individuals were sensitive to the utility of receiving antihypertensive treatment. Treatment of high-risk individuals was highly cost-effective, such that it was the dominant strategy in the oldest age group, and resulted in incremental costs per QALY ranging from pound 34 to pound 265 in younger age groups. Policy decisions about which patients to treat depend on whether a life-expectancy or cost-effectiveness perspective is taken. Treatment increases life expectancy in all strata of age, sex, and cardiovascular risk. However, younger individuals stand to gain proportionately more from blood pressure treatment than do the elderly. In terms of cost-effectiveness, patients at high risk of cardiovascular disease are a highly cost-effective group to treat. In patients at lower risk of cardiovascular disease, consideration should be given to issues of patient preference and cost.