Although the exact role of MMP-9 in atherosclerosis remains controversial [20], MMP-9 activity has been found to be associated with carotid plaque in clinical trials where instability was visualized with ultrasound as a markedly irregular or ulcerated surface, or hypodense or heterogeneous structure [12], or when it was defined retrospectively according to a thin fibrous cap and/or recent intraplaque hemorrhage on histology [13], as well as being indicated by previous stroke or peripheral vascular disease [13]. This evidence concerns the gene MMP9 and peripheral vascular disease.