Pulmonary hypertension is a rare disease of the pulmonary vasculature defined as a mean pulmonary artery pressure > 25 mmHg at rest or 30 mmHg with exercise. Recent therapies such as epoprostenol, bosentan and sildenafil are directed at the arterial vascular bed, causing vasodilatation and reducing pulmonary vascular resistance. However idiopathic pulmonary artery hypertension (IPAH) occurs predominantly in women, with three times the incidence compared to men and this suggests that sex hormones may be involved in the pathogenesis. 17b -oestradiol is a pulmonary vasodilator, proposed to act via an endothelium-dependant pathway, involving nitric oxide (NO) and has also been shown to alter responses to hypoxia. Progesterone is also a pulmonary vasodilator but differs from 17β-oestradiol in having endothelial-dependant and independent processes implicated. Interestingly testosterone has been shown to be a vasodilator in both the coronary and pulmonary circulation with a mechanism of action involving calcium channel blockade of the vascular smooth muscle and without endothelial involvement. In clinical trials testosterone confers symptomatic benefits in patients with coronary heart disease and heart failure, acting as a vasodilator. These observations lend support to the notion that testosterone could be a potential treatment for patients with PAH as vasodilator therapy remains the mainstay of treatment. Other potential beneficial effects of testosterone in the pulmonary circulation include immuno-modulation, altering expression of cytokines and an anti-thrombotic action. In this review the influence of sex hormones on the pulmonary vasculature will be discussed, with specific focus on pulmonary hypertension and the potential treatment of this condition.