The proliferation of vessels within the aneurysm's wall and the intraluminal thrombus of abdominal aortic aneurysm (AAA) may be the main factor responsible for progression and rupture of AAA. The aim of this study was to compare the parameters of the thrombus (size, density, contrast enhancement) measured by computed tomography (CT) with histological assessment of thrombi removed during surgery. 29 patients with AAA were examined with angio-CT. Post-surgery histopathological evaluation of AAA was performed. Slides were stained with markers of B- (CD20) and T-lymphocytes (CD3), and markers of endothelial cells (CD34). Thrombi were enhanced after contrast media administration in angio-CT (p = 0.002). There was a statistically significant correlation between contrast enhancement and the presence of B lymphocytes. Intensity of endothelial cell marker expression significantly correlated with the presence of inflammatory T- and B-cells. No statistical significant correlation was found between contrast enhancement of the thrombus and markers of endothelial cells. The accumulation of inflammatory cells in the wall of AAA thrombus results in the formation of new vessels which participates to the instability of the thrombus and AAA wall. Assessment of the inflammation and neovascularization in the wall and thrombus of the AAA might be an important factor in monitoring the progression and the risk of aneurysm's rupture.