Pulmonary arterial hypertension (PAH) is a condition that is characterised by increased pulmonary arterial pressure and vascular resistance that can lead to right ventricular failure and death. A variety of disturbances in pulmonary vascular endothelial and smooth muscle function are present in PAH, including reduced production of vasodilator and antiproliferative substances, such as nitric oxide and prostacyclin, and an overproduction of mitogens, such as endothelin. As a result of these observations, therapies have been developed for PAH that specifically target these pathogenic processes, including prostacyclin analogues and endothelin receptor antagonists. This article reviews iloprost inhalation solution, the most recently approved form of prostacyclin therapy that is delivered directly to the lungs by inhalation.