A sexually dimorphic pattern of blood pressure, in which the male develops higher blood pressure than the age-matched female, has been observed both in human subjects and in laboratory animals. The mechanism(s) of this sexual dimorphism of blood pressure are not completely understood. This review summarizes sex differences in the epidemiology of hypertension in humans, the role of gonadal steroid hormones in the regulation of blood pressure of normotensive and hypertensive laboratory animals, and new insights into the molecular basis of the sexual dimorphism of hypertension and hypertensive vascular disease.