The pathogenesis of abdominal aortic aneurysm (AAAs) involves progressive cycles of proteolysis and inflammation, the product of proteolysis driving subsequent inflammation. Little is yet known about the initiating events. We review the specific literature examining the possibility that MMP-2 may be the initial catalyst. Histologically, elastolysis is one of the earliest observable events in aneurysm genesis. Matrix metalloproteinase-2 (MMP-2), as the dominant gelatinase differentially expressed in aneurysmal tissue and cells derived from aneurysms, would be a good candidate. We report the results of in vivo and in vitro experiments, which lend support to the importance of MMP-2 as an aneurysmal initiator.