Clinical aspects and pathology of pulmonary hypertension (PH) in patients with systemic lupus erythematosus (SLE) have been reported to be similar to those in patients with idiopathic pulmonary arterial hypertension (IPAH). To determine whether PH in these patients is similar, we compared the clinical characteristics, hemodynamics at diagnosis, and survival in groups of patients with SLE-PH and IPAH. We reviewed the case records of 20 patients with SLE-PH and 34 patients with IPAH, who had been assessed by echocardiography or right cardiac catheterization at Asan Medical Center, Seoul, Korea, from January 1995 to October 2003. Clinical features, laboratory data, chest X-rays, electrocardiogram results, pulmonary function tests, pulmonary perfusion scans, echocardiographic findings, serologic profiles, and survival were compared in the two groups of patients. The mean follow-up period was 18.1+/-20.6 months for patients with SLE-PH and 33.0+/-23.4 months for patients with IPAH. During follow-up, 12 SLE-PH (60%) and 11 IPAH (32%) patients died. For SLE-PH, the 3-year survival rate was 44.9% and the 5-year survival rate was 16.8%. For IPAH, the 3-year survival rate was 73.4% and the 5-year survival rate was 68.2% (p=0.02). There were no other significant differences in clinical characteristics and laboratory data between the two groups. In contrast to previous reports that the prognosis of patients with pulmonary arterial hypertension associated with collagen vascular disease was better than that of patients with IPAH, we found that the prognosis of patients with SLE-PH was much worse than that of patients with IPAH.