Pulmonary arteriovenous fistula is unusually congenital malformation consisting of an abnormal connection between a pulmonary artery and vein. It may appear as an isolated anomaly or with hereditary hemorrhagic telangiectasis. In the classic form, symptoms and signs are caused by the abnormal right to left shunt. since severe clinical symptoms such as paradoxical embolism, infection, and spontaneous rupture with massive bleeding may occur, surgical treatment is often indicated. Recently we have experienced a surgical treatment of pulmonary arteriovenous fistula in 54 years old housewife. She was admitted in May 1986 with recurrent hemoptysis for 1 month. On admission, the PaO2 was 65.2 mmHg without specific findings. Pulmonary arteriovenous fistula was confirmed by preoperative pulmonary arteriography. A well circumscribed cystic mass was noted in visceral subpleural and inferior lingular segment of left upper lobe. Left upper lobectomy was performed with good results. Histologically angiomatous dilatation of abnormal vessels embedded in lung parenchyma was noted. Postoperative PaO2 was 90 mmHg. Postoperative results were good.