OBJECTIVE Functional tricuspid regurgitation (FTR) is the most common type of tricuspid insufficiency and occurs approximately in 30% of patients with mitral valve disease. The major etiologic factor in the triggering of right ventricular dilation and thus causing functional tricuspid regurgitation, is pulmonary artery hypertension secondary to mitral valve disease. We aimed to analyze long-term outcomes of patients with mild tricuspid regurgitation at the time of mitral valve replacement. METHODS Sixty-six patients with mild tricuspid insufficiency who underwent mitral valve replacement were included in this observational retrospective study. Mean follow-up time was 8.3 ± 0.7 years. Patients whose tricuspid regurgitation remained unchanged or decreased following operation were enrolled to group 1 (n=32), patients whose tricuspid regurgitation increased were included to group 2 (n=34) and data were compared statistically with t-test, Mann-Whitney U, Chi-square and Fisher Exact test. Multiple regression analysis was performed to determine independent risk factors for FTR progression. REESULTS:Preoperatively female gender (p=0.02), body surface area (p=0.04), left atrium diameter (p=0.01), functional capacity (p=0.03), right ventricle diameter (p=0.04), and left ventricle mass index (p=0.04) were found to be statistically significant between groups. In the follow-up; functional capacity, grade of tricuspid insufficiency, pulmonary artery pressure, vena contracta width (p<0.001), TAPSE (tricuspid annular plane systolic excursion index) (p=0.04), annulus diameter (p=0.02), right ventricle diameter (p=0.01), left ventricle mass index (p=0.05), and ejection fraction (p=0.02) were found to be statistically different between groups. In multiple logistic regression analysis; preoperative LA diameter (OR=5.05; 95% CI:1.49-17.12; p=0.009) and female gender (OR=10.93; 95% CI:1.77-67.31; p=0.01) were found as independent risk factors for FTR progression. CONCLUSIONS This study revealed that mild FTR might advance to moderate to severe grade in more than half of the patients in the follow-up. Thus, surgical approach to even mild FTR should be individualized based on patient's risk assessment.