Objectives: This study investigated the long-term effects of bosentan, an oral endothelin ETA/ETB receptor antagonist, in patients with pulmonary arterial hypertension (PAH) exclusively related to connective tissue diseases (CTD). Methods: A total of 53 patients with PAH related to connective tissue diseases (PAH–CTD) in World Health Organization (WHO) functional class III received bosentan 62.5 mg twice a day for 4 weeks and then 125 mg twice a day for 44 weeks in this open non-comparative study. Assessments at weeks 16 and 48 included WHO class, clinical worsening, quality of life (Short-Form Health Survey (SF-36) and health assessment questionnaire (HAQ) modified for scleroderma), and survival (week 48 only). Safety and tolerability were monitored throughout the study. Results: At week 48, WHO class improved in 27% of patients (95% CI 16–42%) and worsened in 16% (95% CI 7–29%). Kaplan–Meier estimates were 68% (95% CI 55–82%) for absence of clinical worsening and 92% (95% CI 85–100%) for survival. Overall changes in quality of life were minimal. There were no unexpected side effects observed during the study. Conclusions: In most patients, bosentan was associated with improvement or stability of clinical status. The 92% estimate for survival at 48 weeks is a significant achievement in this patient population.