Pulmonary arterial hypertension (PAH) is a disease characterized by increased pulmonary pressures and chronic right heart failure. Therapies for moderate and severe PAH include subcutaneous (SQ) and intravenous (IV) prostanoids that improve symptoms and quality of life. However, treatment compliance can be limited by severe side effects and complications related to methods of drug administration. Inhaled prostanoids, which offer the advantage of direct delivery of the drug to the pulmonary circulation without need for invasive approaches, may serve as an alternative for patients unable to tolerate SQ/IV therapy. In this retrospective cohort study we collected clinical, hemodynamic, and functional data from 18 clinically stable patients with World Health Organization group I PAH seen in 6 large national PAH centers before and after transitioning to inhaled treprostinil from IV/SQ prostanoids. Before transition 15 patients had been receiving IV or SQ treprostinil (mean dose 73 ng/kg/min) and 3 patients had been on IV epoprostenol (mean dose 10 ng/kg/min) for an average duration of 113 ± 80 months. Although most patients who transitioned to inhaled treprostinil demonstrated no statistically significant worsening of hemodynamics or 6-minute walk distance, a minority demonstrated worsening of New York Heart Association functional class over a 7-month period. In conclusion, although transition of patients from IV/SQ prostanoids to inhaled treprostinil appears to be well tolerated in clinically stable patients, they should remain closely monitored for signs of clinical decompensation. © 2012 Elsevier Inc. All rights reserved.