A post-traumatic false aneurysm of the thoracic aorta is generally the result of a severe closed chest trauma in which deceleration and compression mechanisms operate on the aortic isthmus. Early diagnosis is difficult except where the lesion progresses to rupture. A not inconsiderable number of incomplete and initially closed tears in the wall of the aortic isthmus escape detection and in due course lead to dilatation of the vessel and false aneurysm. The condition is diagnosed, often accidentally, during aortography. The indications for surgical intervention are given by the aneurysm-specific complications, viz.: rupture penetration, embolization. The operation is performed with the aid of a temporary left-heart bypass; it carries a mortality of 5%.