Background: Matrix metalloproteinases (MMPs) have been implicated in the pathogenesis of arterial aneurysms through increased proteolysis of extracellular matrix proteins. Increased proteolysis due to elevated matrix degrading enzyme activity in the arterial wall may act as a susceptibility factor for the development of coronary aneurysms. Plasmin strongly stimulates pro-MMP enzyme conversion to the active form. Plasmin hyperactivity due to decreased plasminogen activator inhibitor-1 (PAI-1) may cause MMP over activity and coronary aneurysms. The aim of this study was to investigate the association between PAI-1 and presence of coronary aneurysms.