An inflammatory aortitis is a common component of many autoimmune and infectious diseases. For example, giant cell arteritis is characterized by a chronic inflammatory infiltrate with giant cell formation. Aortic involvement occurs in 10 to 15% of patients. Usually the presenting symptoms are lower extremity claudication. However, aortic aneurysms and other arterial aneurysms have been reported.’Rheumatoid aortitis occurs in 5% of patients with rheumatoid arthritis. Here, thoracic and abdominal aortic aneurysms (AAA) are frequent. Though rare, in 1996, syphilitic aortitis has occurred in 66% of patients with the formation of saccular or fusiform aneurysms in the ascending, transverse, and descending thoracic aorta. In each instance, the histology is characterized by an infiltration of the aortic wall by lymphocytes, plasma cells, histocytes, and giant cells, depending upon the underlying disease. The inflammation is localized to the media and adventitia in the majority of cases. In some instances, there is an associated perivascular inflammation of the vasa vasorum and endarteritis (see TABLE I). An unusual clinical entity, inflammatory abdominal aortic aneurysm (IAAA) is not associated with any known arteritis, yet histologically IAAA bears many similar inflammatory characteristics. Furthermore, inflammation also plays a role in the pathogenesis of atherosclerosis. Hansson and others have carefully studied atherosclerotic plaques and shown that macrophages and T-cells are important components of this disease process.”’However, the precise relationship between the progression of the atherosclerotic plaque and the inflammatory cells is only now being investigated. Thus, there is mounting evidence of an immune response in several forms