Overviews of randomized controlled trials and prospective observational studies provide the most reliable data on the association between blood pressure and coronary heart disease (CHD). The totality of evidence indicates a strong association between blood pressure and CHD, which is continuous down to levels of at least 115 mm Hg systolic. Overall, for those 60 to 69 years of age, a 10 mm Hg lower systolic blood pressure is associated with about one-fifth lower risk of a CHD event. The size and shape of this association is consistent across regions, for males and females, and for fatal events as well as nonfatal myocardial infarction. Trials comparing active treatment to placebo or no treatment have demonstrated that the benefits of blood pressure lowering with different classes of drugs (e.g., diuretics, beta-blockers, ACE inhibitors, calcium antagonists) are broadly similar, with approximately one-fifth reduction in CHD. ACE inhibitors achieve this with relatively modest blood pressure reductions, but the size of the reduction for calcium antagonists remains uncertain and appears somewhat less than expected from the blood pressure reduction. Trials confirm the expectation from cohort studies of benefits increasing with the amount of blood pressure lowering, and benefit accruing among those with average or even below average blood pressure. Observational data suggest that the proportional association is attenuated with age, but attenuation is less evident in trial data. However, in both cohort studies and clinical trials, CHD risk differences associated with a given blood pressure difference increase with age. The important points to emerge from this review are, first, that the relative benefits of blood pressure lowering for CHD prevention are likely to be consistent across a range of different populations. Second, there is likely to be considerable benefit with blood pressure lowering below "traditional" hypertension thresholds, especially in those with high absolute risk. Third, initiating and maintaining the maximum tolerated blood pressure reduction is a more important issue than choice of initial agent. Finally, and most importantly, the large majority of people have suboptimal blood pressure (e.g., systolic > 115 mm Hg) and so initiatives to lower blood pressure population-wide are an essential adjunct to targeted treatment programs.