A 74-year-old man who went into shock following an acute hemomediastinum and left hemothorax was operated on. Postoperative angiographies revealed a saccular aneurysm of the left bronchial artery of 2.0 cm in diameter. Sixty days after the initial operation, the aneurysm was resected under F-F bypass. A saccular aneurysm was found at the root of the left bronchial artery, which had a very short segment between the aneurysm and the aorta. Pathological study of aneurysm revealed thinning of the wall and lack of tunica media.