We report an extremely rare case of pulmonary artery dissection caused by an abrupt rupture of an aortic arch aneurysm into the pulmonary artery. An asymptomatic 80-year-old man was admitted to our hospital for elective surgical repair of aortic arch aneurysm. After admission, sudden onset of hoarseness and dyspnea developed. Echocardiography demonstrated an intimal flap in the pulmonary artery and abnormal shunt flow from aortic arch aneurysm into the pulmonary artery. At surgery, the pulmonary artery dissection involved the main pulmonary artery and both major branches. Total arch replacement and pulmonary artery reconstruction were successfully performed.