Sex hormones are essential in the development of the biological and physiological sexual characteristics of males and females. However, it is well known that they also play an important role in modulating cardiovascular regulation, particularly with regard to regulation of arterial pressure. Recent comparative examinations of blood pressure regulation in healthy men and women have increased our understanding regarding normal blood pressure control and how sex /sex hormones might influence the development of cardiovascular diseases such as hypertension. Previous studies have shown that, under the age of 40, men and women do indeed regulate resting blood pressure differently. The sympathetic nervous system is central to blood pressure regulation in humans; despite this, basal levels of muscle sympathetic activity (MSNA, an estimate of central sympathetic outflow) are not related to resting blood pressure in either men or women. How can this be when MSNA causes vasoconstrictor tone? Interestingly, in young men MSNA is positively related to peripheral vascular resistance but inversely related to cardiac output. Consequently, men with high MSNA have a high vascular resistance but a lower cardiac output. This balance negates the effect of MSNA on resting blood pressure in men; so men with high MSNA can have a normal resting blood pressure. However, this balance does not exist in young women. In young pre-menopausal women, MSNA is not related to total peripheral resistance or cardiac output. Thus, it appears that basal levels of MSNA contribute little to resting peripheral vasoconstrictor tone. Importantly, this difference between men and women appears to change with age and menopausal status. In postmenopausal women, MSNA becomes directly related to peripheral vascular resistance and blood pressure. This provides strong evidence that sex and sex hormones might modulate how MSNA affects resting blood pressure.