BACKGROUND AND OBJECTIVES: Pulmonary arterial hypertension (PAH) is a rare disease with a poor prognosis. The aim of this study was to characterize PAH in pediatric patients by evaluating the patients demographics, clinical and hemodynamic variables, treatments, and outcomes. SUBJECTS AND METHODS: Sixty-five patients who were diagnosed with PAH at Seoul National University Children's Hospital between January 1985 and August 2007 were retrospectively reviewed. RESULTS: There was no difference in gender distribution (males, 33; females, 32). The mean age at the time of diagnosis was 5.7+/-5.2 years and the mean follow-up period was 6.3+/-5.5 years. The major causes of PAH were congenital heart disease (CHD) in 32 patients (49.2%) and idiopathic PAH in 11 patients (16.9%). The most common presenting symptom was dyspnea in 44 patients (67.7%). The mean cardiothoracic ratio was 58.9+/-8.3%, which decreased to 55.9+/-8.3% after vasodilator therapy (p=0.011). The mean pulmonary arterial pressure at the time of cardiac catheterization was 59.7+/-18.7 mmHg and the mean pulmonary vascular resistance was 14.9+/-9.7 wood units . m2. Forty-three of 65 patients (66.2%) had vasodilator therapy (prostacycline, sildenafil, and bosentan). A statistically significant decrease in tricuspid valve regurgitation velocity (4.8+/-0.8 m/sec vs. 3.6+/-1.0 m/sec, p=0.001), and an increase in diastolic dimension of the left ventricle (28.3+/-12.1 mm vs. 33.2+/-10.2 mm, p=0.021) on echocardiography before and after vasodilator therapy was demonstrated. The 5-, 10-, and 15-year survival rates were 96%, 92% and 65%, respectively. Six of 65 patients (9.2%) with PAH died. There was no significant correlation between outcome and the immediate response to the vasodilators. CONCLUSION: PAH is a devastating disease which is rare in children. PAH in children has a variable pattern cause and progression, the confirmation of which requires analysis of detailed registries from nationwide hospitals.