The most frequent chest X-ray finding of descending thoracic aortic aneurysm is an enlargement of medial mediastinum. Haemoptysis caused by thoracic aortic aneurysm is rare and, normally, when it occurs, it is due to an aorto-bronchopulmonary fistula. We report the case of an 88 year-old male, heavy smoker with arterial hypertension, who had been operated on for abdominal aneurysm five years before, whose unique symptom was scant haemoptysis and radiologically presented a cavity mass in the upper left lobe. Autopsy revealed that the pulmonary cavity mass was due to a descending thoracic aortic aneurysm.