Objective: To determine if treatment with hydroxymethylglutaryl-coenzyme A reductase inhibitors (statins) can influence the development of experimental abdominal aortic aneurysms (AAAs). Summary Background Data: AAAs are associated with atherosclerosis, chronic inflammation, and matrix metalloproteinase (MMP)-mediated connective tissue destruction. Because statins exert antiinflammatory activities independent of their lipid-lowering effects, these agents may help suppress aneurysmal degeneration. Methods: C57Bl/6 wild-type and hypercholesterolemic apoE-deficient mice underwent transient perfusion of the aorta with elastase followed by subcutaneous treatment with either 2 mg/kg simvastatin per day or vehicle. Aortic diameter (AD) was measured before and 14 days after elastase perfusion. The extent of aortic dilatation (ΔAD) was determined with AAAs defined as ΔAD >100%. Results: Wild-type mice treated with simvastatin exhibited a 21% reduction in ΔAD and a 33% reduction in AAAs compared with vehicle-treated controls. Suppression of AAAs in simvastatin-treated mice was associated with preservation of medial elastin and vascular smooth muscle cells, as well as a relative reduction in aortic wall expression of MMP-9 and a relative increase in expression of TIMP-1. In hypercholesterolemic apoE-deficient mice, treatment with simvastatin was associated with a 26% reduction in ΔAD and a 30% reduction in AAAs. Treatment with simvastatin had no effect on serum cholesterol levels in either normal or hypercholesterolemic mice. Conclusions: Treatment with simvastatin suppresses the development of experimental AAAs in both normal and hypercholesterolemic mice. The mechanisms of this effect are independent of lipid-lowering and include preservation of medial elastin and smooth muscle cells, as well as altered aortic wall expression of MMPs and their inhibitors.