BACKGROUND Surgical management of the mitral valve (MV) in patients with mild-to-moderate mitral dysfunction undergoing aortic valve replacement is still controversial. We investigated the echocardiographic data from patients with mild-to-moderate mitral dysfunction who did not undergo MV surgery. METHODS From January 1989 to June 2012, a total of 2731 patients underwent aortic valve replacement. Among these, 560 patients with mild-to-moderate mitral dysfunction were screened. Of these, 292 patients (61.9 ± 13.0 years; 113 females) who had not undergone MV surgery formed our study cohort. Survival, valve-related complication, and echocardiographic data were evaluated. RESULTS There were three early deaths. During the mean follow-up period of 56.9 ± 46.5 months, there were 23 late deaths and 28 valve-related complications. Valve-related event-free survival at 5 years was 85.9% ± 2.4%. In serial postoperative echocardiographic evaluations (mean follow-up duration: 40.8 ± 44.5 months), 21 patients experienced a progression in late mitral dysfunction. At 5 years, 88.8% ± 2.7% of patients did not suffer from late mitral dysfunction. Based on multivariate analysis, rheumatic pathology of MV (Hazard Ratio: 3.88, 95% confidence intervals 1.60-9.39, p = 0.003) was an independent predictor of late mitral dysfunction. CONCLUSIONS Conservatively treated patients with mild-to-moderate mitral dysfunction exhibited acceptable clinical outcomes. Rheumatic pathology of MV is associated with a higher risk of progressive native MV dysfunction.