A twenty four-year-old female patient had suffered progressive dyspnea for 6 years until death. She denied any symptoms suggestive of connective tissue disease, or deep vein thrombosis. She suffered an episode of pontine infarct in 1995. Four years after diagnosis of primary pulmonary hypertension, she died of sudden death during hospitalization. Gross features of pulmonary arteries at autopsy were as follows: left main pulmonary artery showed dilation of the lumen and thickening of the wall, and right main pulmonary artery was markedly dilated and contained fresh thrombus. Hematoxylin and eosin-stained sections of lung tissue showed plexiform lesions of pulmonary arteries, complete luminal obliteration of pulmonary arterioles and dilated lesion of pulmonary arterioles, and capillaries. This patient represents a typical case with a primary pulmonary arteriopathy with plexiform lesions with thrombotic lesion, demonstrating the importance of thrombosis in situ in the pathogenesis of primary pulmonary hypertension. To our knowledge, this is the first autopsy report on the primary pulmonary hypertension in Korea.