SUMMARY Aortic infarction was observed in 21 of 34 cases of dissecting aortic aneurysm. This lesion occurred as a central zone of necrosis with preserved elastic laminae, sparing media adjacent to the true and false lumens. In cases where the false lumen was occluded, the central infarction extended to this lumen. The infarction followed rather than preceded dissection, took approximately 48 hours to develop, and did not organize with time. The lesion occurred exclusively in the thoracic aorta, and bore no relationship to medial cystic necrosis. Present surgical therapy does not extirpate these areas, and the implication of these lesions in terms of management remains to be determined.