Although human abdominal aortic aneurysm (AAA) is characterized with eccentric formation of intraluminal thrombus, its molecular mechanism has not been studied. Here, we investigated the potential relationship between tissue factor (TF) known to play a major role in thrombus formation, and Egr-1, shear stress-inducible transcription factor which seems to be upreguated by turbulent flow within AAA. During the electric surgery, specimens were taken from the thrombus-covered and thrombus-free wall in each of seventeen AAA patients, and appropriately prepared to analyze the expression of tissue factor and Egr-1. In the immunohistochemical analysis, Egr-1 and TF were highly expressed in vascular smooth muscle cells in the thrombus-covered wall. Their expression levels were quantified using real-time quantitative polymerase chain reaction, where both TF and Egr-1 genes were significantly upregulated in thrombus-covered walls as compared with thrombus-free walls. When their association was analyzed, the induction fold and absolute expression level of Egr-1 were found to strongly correlate with those of TF respectively (induction fold: p<0.05, r=0.60, expression level: p<0.001, r=0.69). These results suggest that differential induction of Egr-1 in aneurysm wall is responsible for the TF upregulation in discrete aortic wall, subsequently leading to the eccentric thrombus formation in human AAA. Furthermore, such an increase of Egr-1 expression in aneurysm wall might contribute to the inflammation as well, in that adenovirus-mediated Egr-1 overexpression upregulated a variety of inflammation-related genes as well as TF in vascular smooth muscle cells and endothelial cells.