A patient with relapsing polychondritis and thoracic and abdominal aortic aneurysms is described. The aortic changes were due to aortitis, which primarily involved the media, with increased vascularization, perviascular infiltration of mononuclear cells, increased amounts of collagen and decreased amounts of elastic tissue and sulfated acid mucopolysaccharides. Aortic aneurysms frequently occur in relapsing polychondritis; they are usually in the ascending aorta but may be multiple and involve the abdominal aorta; involvement of the ascending aorta results in aortic regurgitation and left ventricular failure, and involvement of the abdominal aorta may be clinically silent and result in fatal rupture.