Based on individual patient data, we performed a quantitative overview of trials in hypertension to investigate to what extent lowering of systolic blood pressure (SBP) and diastolic blood pressure (DBP) contributed to cardiovascular prevention. We selected trials that tested active antihypertensive drugs against placebo or no treatment. Our analyses included 12,903 young (30 to 49 years of age) patients randomized in 3 trials and 14,324 old (60 to 79 years of age) and 1209 very old (> or =80 years of age) patients enrolled in 8 trials. Antihypertensive treatment reduced SBP/DBP by 8.3/4.6 mm Hg in young patients, by 10.7/4.2 mm Hg in old patients, and by 9.4/3.2 mm Hg in very old patients, respectively, resulting in ratios of DBP to SBP lowering of 0.55, 0.39, and 0.32, respectively (P=0.004 for trend with age). In spite of the differential lowering of SBP and DBP, antihypertensive treatment reduced the risk of all cardiovascular events, stroke and myocardial infarction in the 3 age strata to a similar extent. Absolute benefit increased with age and with lower ratio of DBP to SBP lowering. Furthermore, in patients with a larger-than-median reduction in SBP, active treatment consistently reduced the risk of all outcomes irrespective of the decrease in DBP or the achieved DBP. These findings remained consistent if the achieved DBP averaged <70 mm Hg. In conclusion, our overview suggests that antihypertensive drug treatment improves outcome mainly through lowering of SBP.