In a review of 17 cases in which the CT diagnosis of abdominal aortic aneurysm rupture was prospectively made and for which surgical correlation was available the CT diagnosis was correct in 10 and incorrect in seven. Two of the false positives were retrospectively reinterpreted as negative for rupture. Characteristics of 10 surgically confirmed cases revealed a spectrum of appearances not always in agreement with prior published reports, probably due to the age and magnitude of the aortic leaks at the time of diagnosis. The most common characteristic of aneurysm leak (eight of 10 cases) was an abnormal soft tissue collection located adjacent to the posterior aspect of the aneurysm, a sign not previously emphasized in other reports. Renal displacement was also a valuable sign but was present in only three cases, all of which had large hemorrhages. Other characteristics of aortic rupture such as density of the collection and sharpness of its margins were not found to be generally useful.