OBJECTIVE Pulmonary arterial hypertension associated with connective tissue disease (PAH-CTD) is difficult to manage, and has a poor prognosis. The phosphodiesterase-5 inhibitor sildenafil citrate enhances vasodilatation, has antiproliferative effects, and is effective in the treatment of PAH. We examined the efficacy and safety of oral sildenafil in patients with PAH-CTD. METHODS In a 12-week, double-blind study (SUPER-1), 278 patients with PAH were randomized to oral placebo, sildenafil 20 mg, sildenafil 40 mg, or sildenafil 80 mg 3 times daily (tid). In a post-hoc subgroup analysis of 84 patients with PAH-CTD, exercise capacity, hemodynamic measures, World Health Organization functional class, and tolerability were assessed. RESULTS Forty-five percent of the patients had scleroderma, 23% had systemic lupus erythematosus, and the rest (32%) were categorized as other. Patients were predominantly functional class II (38%) or III (61%) at baseline. Sildenafil-treated patients exhibited mean increases in 6-minute walk distance at Week 12 of 42 m (95% CI 20, 64) for 20 mg, 36 m (95% CI 14, 58) for 40 mg, and 15 m (95% CI -24, 54) for 80 mg, while placebo-treated patients exhibited a mean decrease of 13 m (95% CI -36, 10). Improvement of at least 1 functional class occurred in 29%-42% of sildenafil-treated patients, compared to 5% for placebo. Significant improvements in mean pulmonary arterial pressure and pulmonary vascular resistance were observed with sildenafil 20 mg, and sildenafil was generally well tolerated. CONCLUSIONS In patients with PAH-CTD, sildenafil improves exercise capacity, hemodynamic measures (at the 20 mg dose), and functional class after 12 weeks of treatment.