Background: Intravenous prostacyclin (iv PGI) and inhaled Iloprost (inh ilo) are established therapies in pulmonary arterial hypertension (PAH), however comparative data are lacking. Methods and patients: We performed a long-term open label comparison trial of iv PGI or high dose inh Ho in 24 patients with severe PAH: 12 patients (9 female, 40 +/- 14 years, 10 idiopathic PAH, 2 PAH in connective tissue disease CTD) received iv PGI, whereas 12 patients (7 female, 43 +/- 12 years, 5 IPAH, 6 CTD, 1 porto-pulmonary hypertension) were commenced on inh ilo with a median dose of 120 mu g/24 h. Haemodynamic parameters and 6 min walking distance (6MWD) at baseline did not differ between both groups. Results: After 3 months therapy, patients on iv PGI showed a significant increase in 6MWD from 220 to 280 m (p < 0.01), whereas patients on high dose inh ilo increased 6MWD from 200 to 275 m (p < 0.05). The event free follow up was 23 [1-76] months in the iv PGI2I group, and 16 [7-38] months in the high dose inh ilo group (p < 0.05). Patients with a 6MWD >= 300 m after 3 months therapy had a significantly longer event free follow up [16 vs. 35 months; p < 0.004]. Conclusion: In this patient population with severe pulmonary hypertension of different etiologies, event free follow up on treatment with iv PGI is significantly longer compared to high dose inh Ho. The 6MWD after 3 months treatment might be predictive for long term outcome. (C) 2010 Elsevier Ltd. All rights reserved.