Aims: Our aim was to compare hemostatic and inflammatory mechanisms in abdominal aortic aneurysm (AAA) patients after open surgery (OPEN) and endovascular AAA repair (ENDO). Subjects and Methods: From the 32 consecutive AAA patients recruited, 17 represented ENDO and 15 OPEN. The intra-aneurysmal thrombus was removed during OPEN, but stayed intact after ENDO. The pre-operative volume of the intra-aneurysmal thrombus was calculated from computed tomography images. Markers of coagulation and inflammation were studied pre-operatively, at one, two, three, four and seven days and at three months postoperatively. Results: Preoperative upregulation of F 1 + 2, TAT and D-dimer was evident in both groups. The volume of intra-aneurysmal thrombus correlated with CRP (β=0.62, p=0.001), IL-6 (β=0.60, p=0.001) and PAI-1 ag (β=0.51, p=0.007). Surgery further enhanced inflammation, coagulation and fibrinolysis. IL-6 increased in both groups, but the increases of CRP and PIIINP were higher in the OPEN group. Postoperative CRP correlated with the intra-aneurysmal thrombus volume in the ENDO group. At three months D-dimer (p<0.05) was higher than pre-operatively in the ENDO, in contrast to the OPEN group. Conclusion: Preoperatively both prothrombotic and fibrinolytic mechanisms are activated in patients with AAA. Intraluminal thrombus induces prothrombotic and inflammatory interactions, which persist after endovascular aortic aneurysm repair.