The pathogenesis of abdominal aortic aneurysms (AAAs) is unknown. We hypothesize that the autoimmune disease process plays a key role in the development of AAAs. Both cellular and humoral immunity is involved in the pathogenesis of AAAs. Triggers of autoimmunity are multifactorial. Certain HLA typing is closely related to AAAs, and a certain viral infection may have a potential role in the etiology of AAA via a molecular mimicry mechanism. The autoantigen is located in the microfibrillar compartment of the aortic wall as a normal structure. Patients with AAA are immunoreactive with this novel structural protein. If in the future the autoantigen is fully elucidated, serum testing to detect antibody against the autoantigen can be performed.