Pulmonary arterial hypertension (PAH) is a progressive disease in which increased pulmonary arterial pressure and remodelling eventually lead to right heart failure and death. Idiopathic and familial PAH occur far more frequently in women than in men. Historically, investigations into this gender bias have been impeded because female gender and oestrogens paradoxically protect against PAH in commonly used rodent models. However, recent descriptions of female gender-specific murine models of PAH have led to an increased understanding of the role of oestrogens in disease development. Specifically, oestrogen metabolism has been highlighted as playing an important role in disease development, and the oestrogen-metabolizing enzyme CYP1B1 may represent a novel therapeutic target. In addition, emerging evidence suggests that sex hormones may have direct effects on the right ventricle independent of haemodynamic effects. This review discusses our current understanding of the role of sex hormones in the development of PAH.