A 55-year-old man was admitted following the discovery of a radiographic abnormality. A chest radiograph and computed tomography showed a subpleural nodule in the lingular division of the left lung with a dilated pulmonary vein. A pulmonary arteriograph showed no abnormal pulmonary artery in the pulmonary arterial phase, no abnormal pulmonary vein in the pulmonary venous phase, but an abnormal artery (left lateral thoracic artery) from the left subclavian artery with a fistula to the pulmonary vein. A left lateral thoracic arteriograph clearly showed that this artery was dilated and formed a fistula with the pulmonary vein. The patient was given a diagnosis of systemic arterio-pulmonary venous fistula. Such cases are very rare, but some cases with hemoptysis have been reported. The patient was given the option of treatment by operation or embolization, but he refused any therapy.