Aneurysm of a saphenous vein graft (SVG) is a rare but fatal complication of coronary artery bypass graft (CABG) surgery. The development of SVG aneurysms appears usually about 10-20 years after the operation at an estimated rate of <1%. A 68-year-old male was referred to the emergency department after frequent episodes of dyspnea, chest pain and hemoptysis. He previously had CABG surgery one year before. The physical examination was normal. Chest radiogram showed a left pulmonary midzone mass. CT-angiogram demonstrated a large aortic pseudoaneurysm (6.36 x 6.06 cm) in the middle part of the ascending aorta. After sternotomy, the ascending aorta above sinotubular junction near the origin of brachiocephalic artery was resected and replaced with a tube graft. The patient was transferred to ICU with stable hemodynamic status. SVG aneurysm should be considered while encountering mediastinal mass or undiagnosed cardiopulmonary symptoms in patients with a previous history of CABG because of its rarity and overlap of symptoms with other thoracic, pulmonary, and cardiac diseases. Surgery seems to be the treatment of choice to reduce the risk of rupture and embolism.