Background: Predictors of aortic dilatation are not well-described in patients with bicuspid aortic valve (BAV). Changes in extracellular matrix composition in the aortic wall may play an important role. Our study aimed to examine the relationship between ascending aortic dilatation and biochemical markers for collagen metabolism, such as matrix metalloproteinase-2 (MMP-2) and matrix metalloproteinase-9 (MMP-9) levels in patients with BAV. Methods: All patients underwent cardiac echocardiography using a standard protocol, and aortic measurements were made in end-diastole. One hundred twelve BAV patients with no or mild valvular impairment were recruited and grouped according to the aortic dimensions corrected for body surface area (BSA) and age. There were 54 patients with dilated ascending aorta (Group 1) and 58 patients with nondilated ascending aorta (group 2). The plasma levels of MMP-2 and MMP-9 were determined by ELISA. Results: The mean ascending aorta diameter was 4.49 +/- 0.49mm in group 1 and 3.51 +/- 0.46mm in group 2 (P<0.001). There were no significant difference in gender, BSA, presence of hypertension, diabetes mellitus, hyperlipidemia, and smoking between the 2 groups. Nevertheless, no significant difference was observed in the levels of MMP-2 and MMP-9 between the 2 groups. The ascending aorta diameter correlated significantly with age (r=0.438 P<0.001). No significant correlation was observed between plasma MMP-2 and MMP-9 concentration and ascending aorta diameter, respectively (r=0.005 P=0.58, r=0.106 P=0.07). Multivariate analysis showed that age was independent predictor of aortic dilatation (P0.001). Conclusion: Age was an independent predictor of aortic dilatation in patients with BAV, whereas MMP-2 and 9 levels were not relevant by aortic dilatation.