This article examines the rationale for the differences in the guidelines for hypertension management of four national or international bodies: the Joint National Committee (JNC-V). The World Health Organization/International Society of Hypertension (WHO-ISH), the British Hypertension Society (BHS), and the New Zealand guidelines. These guidelines agree on many aspects of management, but differ on two very important pointsthe drugs of first choice for hypertension, and the indications for drug treatment of uncomplicated mild hypertension. JNC-V recommends treatment routinely of all people with a sustained blood pressure of 140/90 mm Hg, whereas the BHS guidelines advise treatment routinely at 160/100 mm Hg. Such differences in the threshold for treatment have a major impact on the proportion of the adult population to be treated, and on the benefit from treatment. JNC-V was heavily influenced by the Hypertension Detection and Follow-up Program (HDFP), which appeared to show a large benefit from the treatment of uncomplicated mild hypertension, whereas the BHS guidelines were influenced by the Medical Research Council (MRC) Trial, which showed a very small benefit. However, the apparent differences in absolute benefit between these, and other, randomized controlled trials is related entirely to differences in the absolute cardiovascular risk of the populations studied. In populations and in individual patients the benefit from antihypertensive treatment is determined by the absolute cardiovascular risk. Blood pressure by itself is a very weak predictor of risk or benefit from treatment. In uncomplicated mild hypertension the need for drug therapy should be based on the absolute risk of cardiovascular complications, estimated by considering age, sex, serum cholesterol level, diabetes mellitus status, and smoking habits, in addition to blood pressure. Doctors cannot estimate absolute risk accurately informally or intuitively, and the next generation of guidelines should incorporate a simple but accurate method for estimating cardiovascular risk, similar to that in the New Zealand guidelines. The decision to treat, or not treat, uncomplicated mild hypertension should be based on a formal estimate of absolute cardiovascular risk and not on an arbitrary blood pressure threshold. As regards drugs of first choice, the available evidence supports strongly the stance of JNC-V and JNC VI that diuretics and β- blockers should be preferred unless they are contraindicated, or unless there are positive indications for other drug classes.