Neither blood pressure measurements nor other clinical features permit an entirely adequate characterization of individuals having mild hypertension. However, although any definition of mild hypertension is arbitrary, the concept is firmly established in clinical practice and such classifications can prove useful as operational diagnoses. The relative risk of subjects with mild hypertension is less than that in subjects with moderate or severe hypertension. However, the prevalence, and thus the population-attributable risk, of mild hypertension is far greater than that of the more severe forms of hypertension. Thus, mild hypertension clearly constitutes a public health problem of considerable importance. Increasing evidence suggests that antihypertensive drug therapy can not only normalize the blood pressure of patients with mild hypertension but can also reduce the morbidity and mortality that occur in the untreated state.