In a series of 28 patients with suspected ruptured thoracic aorta, only three were shown to have sustained such an injury. To minimise the number of negative examination, the importance of optimising the initial radiological examination of the chest is discussed along with the importance of visualisation of the descending aorta. The signs that lead to the suspicion of rupture of the aorta are numerous and non specific and indicate some change in the mediastinum which could be significant in the given clinical context. This paper wishes to emphasise a negative sign, namely visibility of the descending aorta.