BACKGROUND The development of abdominal aortic aneurysm (AAA) is probably influenced by many factors. The role of some of these factors, such as intraluminal thrombus (ILT) or cystatin C serum levels, remains controversial. Proving their influence could have therapeutic implications for some patients with AAA. Associations between the rate of increase in diameter of an aneurysm and ILT, as well as other factors, including biochemical factors (C-Reactive Protein - CRP, cystatin C), age, sex, and comorbidities, could predict disease progression in individual patients. MATERIAL AND METHODS Seventy patients with small AAA were included into the study. The patients were followed using ultrasound and CT imaging. We evaluated aneurysm dimensions and aneurysm wall thickness, as well as ILT and its dimensions, aneurysm wall morphology, CRP, and cystatin C. RESULTS We observed significant growth of AAA and thinning of aneurysmal wall. Aneurysms over 4 cm grew significantly faster in the second year of observation. ILT grew together with AAA size. Age, sex, smoking, dyslipidemias, or controlled arterial hypertension had no influence on aneurysm progression rate. Changes in serum of CRP concentration did not reach statistical significance, but cystatin C levels did. CONCLUSIONS Presence and size of ILT, wall thickness, and cystatin C levels may be considered in prediction of AAA progression. ILT might exert a protective influence on the risk of aneurysm rupture. However, larger aneurysms containing larger thrombi grow faster and their walls undergo more rapid degradation, which in turn increases the risk of rupture. This matter requires further studies.