Pulmonary arterial hypertension (PAH) is a chronic condition of elevated pulmonary arterial pressures with associated increases in pulmonary vascular resistance leading to right ventricular failure, which was almost uniformly fatal prior to the introduction of pulmonary hypertension specific therapy. Systemic prostacyclin analogs are the first PAH-specific therapies to be made available and are typically recommended as first-line therapy for subjects with severe disease. Treprostinil is a newer prostacyclin analog similar to epoprostenol in its mechanism of action and relative efficacy with the advantage of a longer half life in human serum and room temperature stability. It is unique in that it is available in multiple formulations for alternative routes of delivery, including subcutaneous, intravenous and inhalational routes. Additionally, oral treprostinil is currently under investigation. Both subcutaneous and intravenous forms of treprostinil have demonstrated efficacy in short-term clinical trials and are currently approved for use in subjects with PAH and New York Heart Association functional class (NYHA FC) II-IV symptoms in the USA and for subjects with NYHA FC III and IV in Europe. Inhaled treprostinil has also demonstrated efficacy in short-term clinical trials primarily as add-on therapy and is currently approved for use in subjects with PAH and NYHA FC III-IV symptoms in the USA and Europe. The different formulations of treprostinil have significantly increased the treatment options and opportunities for treatment of patients with PAH.