Amongst the rare causes of haemoptysis rupture of the great vessels is always a possibility. An aorto-bronchial fistula is a rare complication of thoracic aneurysms of the aorta. A fistula starting from a false aneurysm is exceptionally rare. Our observation concerns a patient of 61 with previous vascular problems who was discovered to have a mediastinal tumour following dysphonia and haemoptysis. Aortography and surgical intervention revealed that this was a false aneurysm of the horizontal part of the aorta which had developed a fistula in the bronchus.