Many circulating haemostatic markers have been investigated in relation to the abdominal aortic aneurysm (AAA) size, growth as well as intraluminal thrombus (ILT) size. However, the results of these studies seem to be uncertain and inconsistent. The first aim of the present study was to compare the haemostatic parameters of fibrinolysis and some of thrombotic markers in patients with AAA and controls. We also examined the relationship between those parameters and both maximum aneurysm diameter and intraluminal thrombus thickness. Tissue plasminogen activator (t-PA), plasminogen activator inhibitor (PAI-1), fibrinogen (Fb), D-dimer, prothrombin fragments 1 and 2 (F1+2), thromboxane B2 (TXB2) and lipids profile were measured in 36 patients with AAA and 30 controls. The mean maximum aortic diameter in patients with the AAA was 59±12 mm (range 42-100). The mean ILT thickness was 32±10 mm (range 8-56). Among haemostatic factors, t-PA and D-dimer levels, but not PAI-1, were significantly higher in subjects with the AAA. There was a strong positive correlation between thickness of intraluminal thrombus and maximum aneurysm size (r=0.69, p<0.0001), and the negative relationship between t-PA and ILT thickness (r= -0.53, p=0.001) as well as aneurysm diameter (r= -0.38, p=0.023). Higher plasma concentrations of t-PA and D-dimer support the hypothesis that the secondary fibrinolysis plays an important role in the pathogenesis of the aortic abdominal aneurysm formation. In addition, the negative correlation between t-PA plasma level and ILT thickness suggests that thrombotic/fibrinolysis imbalance may favour accelerated formation of intraluminal thrombus and possibly aneurysm progression.