CASE PRESENTATION: A 62-year-old woman was referred to our hospital for suspected recurrent pulmonary thromboembolism (PE). She complained of dry cough and chest pain for two days. Eighteen months before, she was detected abnormal electrocardiographic (ECG) patterns without any symptoms, and diagnosed as PE with CT and perfusion scan. Since then, she had been treated with warfarin, however, her condition and ECG patterns were unchanged. She never smoked. Her oxygen saturation was 94% on room air, and the other vital signs were normal. A physical examination revealed normal breathing and cardiac sounds, and no edema. Laboratory test values were as follows: white blood cells, 5,660/mm3; hemoglobin, 11.6 g/dl; platelets, 115,000/mm3; serum lactate dehydrogenase, 223 U/l; serum aspartate and alanine aminotransferase, 34 U/l and 19 U/l; serum albumin, 2.8 g/dl; serum C-reactive protein, 0.57 mg/dl; serum D-dimer, < 0.5μg/ml; brain natriuretic peptide, 631.2 pg/ml. Serum protein C and protein S activity were normal, and antinuclear antibody, anti-phospholipid antibody, PR3-ANCA and MPO-ANCA assays were negative. An ECG showed nonspecific T-wave abnormalities. Transthoracic echocardiography revealed normal chamber sizes, normal left ventricular function, and no evidence of the other structural heart diseases. Chest radiograph showed reticular changes in the right middle and lower lung field without volume change. 3D-CT with enhancement showed absent right interlobar pulmonary artery without any other abnormalities of pulmonary artery, and also enlarged inferior phrenic artery. HRCT demonstrated ground-glass opacities, reticular changes, and small cysts in the right middle and lower lobes, compatible with fibrotic NSIP. Lung perfusion scan showed total defect in the right middle and lower lobes. The patient was diagnosed as isolated congenital interruption of the right interloabr pulmonary artery, since chronic PE, structural heart disease, systemic congenital disease and systemic vasculitis were ruled out. Her symptoms disappeared on the 2nd day of admission, and her condition continued to be stable without any treatment.