The natural history of a thoracic aneurysm is usually towards the dissection or free rupture; rarely an aorto-pulmonary fistula can complicate this lesion. We present two cases of Aorto-pulmonary fistula as acute complication of an aneurysm of thoracic aorta; the etiopathology seem to be related to the same mechanism: a dissecting aneurysm of the ascending aorta leading to a secondary fistulation in the main pulmonary artery. In our two cases the diagnosis was suggested by clinical findings and by Doppler-echocardiography. Both patients were managed surgically with success and both survived.