The presence of elevated values of both diastolic and systolic arterial blood pressure is one of the most important risk factors for coronary heart disease, stroke, and heart failure; in patients with hypertension, the pharmacological reduction of blood pressure decreases the risk of adverse cardiovascular events, though the optimal blood pressure goal is still being debated. During recent years there has been an increasing interest in isolated systolic hypertension, both as an independent risk factor for cardiovascular disease and as a clinical entity requiring treatment in its own right. The definition of what constitutes isolated systolic hypertension still remains controversial and arbitrary; the criteria generally used is a systolic blood pressure > or = 140 mmHg and a diastolic blood pressure < 90 mmHg. Not only the cut-off levels used to define isolated systolic hypertension, but also the number of occasions on which blood pressure is measured can significantly affect the prevalence of isolated systolic hypertension in the total population. The use of 24-hour ambulatory blood pressure monitoring is a relatively new method for overcoming transient elevations in blood pressure that often occur during clinic measurement; it has a good reproducibility, is subject to little "white-coat" or placebo effect, and finally provides blood pressure measurements within a subject's normal environment. Borderline isolated systolic hypertension (defined as a systolic blood pressure between 140 and 159 mmHg and a diastolic blood pressure < 90 mmHg) is probably the most common type of untreated hypertension among adults over the age of 60; in the following 20 years, about 80% of patients with borderline isolated systolic hypertension will show progression to definite hypertension with increased risk of development of cardiovascular disease. The increase in systolic and diastolic blood pressure with age is typical of Western societies, while it is not observed among some "unacculturated" populations, who tend to be lean and physically active, with a lower daily sodium intake. Maybe environmental, rather than genetic factors may contribute more to the determination of blood pressure throughout life. Pharmacological treatment of isolated systolic hypertension can lead to a significant reduction in total stroke, coronary heart disease, and cardiovascular disease. The question of which antihypertensive agents are most effective is still to be fully elucidated with specifically addressed trials.