Precise and accurate communication between professionals depends on a consensus regarding concepts and the words used to describe them. The concept of true and false arterial aneurysms is a case in point. At a recent radiology conference, the aortogram of a young man who was involved in a motor vehicle accident showed localized dilatation of the aorta at the aortic isthmus. Contrast material was contained within the aortic lumen by the stretched adventitia of the arterial wall. A transverse radiolucent line, caused by the rolled-up edges of the ruptured intima and media, was seen. There was general agreement that a lumen associated with rupture of all three layers of the aortic wall should be called a false aneurysm, and that dilatation involving all three layers of the wall should be called a true aneurysm. There was disagreement, however, as whether to refer to an injury in which there is disruption of the intima and media with an intact adventitia as a false on a true aneurysm. An investigation into current, authoritative medical sources only served to further confuse the issue. The 22d edition of Dorland’s Medical Dictionary defines a true aneurysm as “an aneurysm in which the sack is formed by the arterial walls one of which, at least, is unbroken”[1]. It defines a false aneurysm as “one in which the entire wall is injured and the blood is contained by the surrounding tissues.” However, the