Background: Vardenafil is a new phosphodiesterase-5 inhibitor that has shown some efficacy in the treatment of pulmonary arterial hypertension (PAH). Objective: To examine the long-term effects of vardenafil in patients with PAH. Methods: A multicentre, open-label study of 1-year's duration was undertaken in 45 patients with PAH to determine the long-term safety and efficacy of vardenafil (5 mg once daily for the first 4 weeks, then 5 mg twice daily) and make a preliminary assessment of its monthly acquisition cost compared with other PAH-active treatments. The patients' clinical features, exercise capacity, WHO functional class and haemodynamic variables were measured at baseline and at 3 and at least 9 months after initiating vardenafil treatment. Results: At the 3 months and a mean (SD) of 14 (3) months (range 9-18) follow-up assessments, the 6 min walking distance was significantly increased from baseline by 70.7 (78.4) m (p<0.001) and 83.4 (91.8) m (p<0.001), respectively. Furthermore, long-term treatment with vardenafil for a mean duration of >1 year was also associated with improvements in haemodynamic parameters, WHO functional class and serum uric acid concentrations. Overall, vardenafil treatment was well tolerated. No patients were withdrawn owing to adverse events and none died during the course of the study. Conclusion: Long-term treatment with vardenafil is well tolerated and has sustained beneficial effects on PAH, as measured by patients' exercise capacity, WHO functional class and haemodynamic parameters.