Abstract Background: Mitral regurgitation (MR) is frequently associated with aortic stenosis. Previous reports have shown that coexisting mitral insufficiency can regress after aortic valve replacement (AVR) while others recommend dealing with examination. Aim: The study aimed to assess the severity of MR before and after aortic valve replacement for aortic stenosis and to define the determinants of its postoperative evolution. Methods: For this purpose, 30 adult patients referred for aortic valve surgery underwent pre- and 1 month postoperative transthoracic echocardiography including 2D, MM, PW, CW and color Doppler examination. Results: Postoperative MR improved in 68.4% of the 19 patients (63.3%) who had preoperative moderate MR (p= 0.002). The effect of the valve size on the postoperative MR was statistically insignificant (0.059) but was significant on regression of the mass (p= 0.001) and drop in mean PG (p= 0.04) across AV. Patients with persistent moderate MR after surgery were all in AF and had significantly larger left atrial size (45± 26 mm), compared to none and a smaller left atrial (37 ±19 mm) in patients in whom MR regressed or disappeared after surgery; respectively, p< 0.05. The postoperative variables associated with moderate MR were peak PG across AV (29.4 ±5.1 vs 38.0 ± 5.7 p= 0.004), mean PG (15.04± 4.4 vs 22.8 ±5.8 p= 0.009) and LVMI (124.7± 19.3 vs 147.2± 31.6 p= 0.065). Conclusion: Preoperative predictors of residual postoperative MR were large LA and AF while the postoperative variables were high peak and mean pressure gradient across the aortic valve and high LVMI.