OBJECTIVE: To determine whether pulmonary arterial hypertension (PAH) is a prognostic factor for mortality in diffuse cutaneous systemic sclerosis (dcSSc), independent of interstitial lung disease (ILD). METHODS: ILD was diagnosed by high-resolution computed tomography and PAH (pulmonary arterial systolic pressure [PASP] > or =45 mm Hg) by echocardiography. All patients with ILD underwent testing for total lung capacity (TLC), forced vital capacity (FVC), and diffusing capacity for carbon monoxide. RESULTS: Eighty-six patients with dcSSc (mean age at diagnosis 44.5 years) were followed up for a median of 72.5 months. ILD was found in 52 patients (60%) and PAH in 18 (21%). ILD was associated with PAH in 15 patients. Seventeen patients died (19.8%), 9 of whom had PAH (P = 0.001) and 10 of whom had ILD (P = 0.99). By multivariate analysis, age at SSc diagnosis and PAH were the only independent predictors of death (hazard ratio [HR] 1.057, 95% confidence interval [95% CI] 1.009-1.109, P = 0.020 and HR 4.09, 95% CI 1.47-11.5, P = 0.007, respectively). Mean TLC and mean FVC were similar in ILD patients with and those without PAH (P = 0.71 and P = 0.40, respectively). Among ILD patients, age at SSc diagnosis and PAH were again the sole predictors of death (HR 1.073, 95% CI 1.003-1.149, P = 0.042 and HR 5.07, 95% CI 1.09-23.8, P = 0.038, respectively). Twenty ILD patients received at least 6 monthly pulses of intravenous cyclophosphamide (CYC). In CYC-treated patients with PAH (n = 8), PASP increased significantly during the CYC regimen (mean +/- SD 55 +/- 14.5 mm Hg; P = 0.015 versus baseline), while TLC remained stable during the same period. CONCLUSION: These results indicate that, independent of ILD, PAH is a major prognostic factor for survival in dcSSc.