Aim. To assess the impact of disturbed extracellural matrix protein balance andmatrix metalloproteinase (MMP) activity on the development of ascending aorticaneurysm (AAA) of varied aetiology.Material and methods. The study included 38 patients with AAA and 17 controlswithout any aortic pathology. In intra-surgery biopsy samples, the levels and activityof MMP-2, MMP-9, fibrillin, elastin, and collagen were measured.Results. Elevated levels of latent MMP-9 and MMP-2 forms were observed inpatients with atherosclerosis and tricuspid aortic valve, compared to controls. Inparticipants with bicuspid aortic valve, the levels of both latent and active MMP-9forms were higher than in controls. In biopsy samples, the elastin-to-collagenratio values were elevated in patients with atherosclerosis (1:1,7) and bicuspidaortic valve (1:1,6).Conclusion. The difference in the MMP levels and activity and the increasedcollagen-to-elastin ratio could be related to the underlying mechanisms of the AAAdevelopment in patients with bi- and tricuspid aortic valve.