The optimal timing of mitral valve surgery in patients with severe organic mitral regurgitation (OMR) and no or mild symptoms is highly controversial. The aim of this study was thus to determine the preoperative predictors of mortality following mitral valve surgery in patients with severe OMR and no or mild symptoms. Preoperative and operative data of 324 patients (65% of male, mean age: 65±13 years) with severe OMR and no/mild symptoms (NYHA class I and II) who underwent mitral valve surgery between 1992 and 2007 were prospectively collected in a computerized database. Mitral valve repair (MVRp) was performed in 132 (41%) and mitral valve replacement (MVR) in 187 (59%) patients. Operative mortality was low for both procedures (whole cohort: n=9, 2.7%; MVRp: n=2, 1.5%; MVR: n=7, 3.7%; p=0.34) but was significantly higher in the patients (n=167, 56%) with impaired preoperative left ventricular ejection fraction (LVEF) (<60%) (5.3% vs. 1.2%, p=0.04). Long-term survival was 93±2% at 5 years and 87±3% at 10 years. Patients with LVEF<60% had significantly reduced long-term survival compared to patients with normal LVEF (5-year: 89±4% vs. 95±5%, 10-year: 80±6% vs. 88±4%, p=0.049). Multivariate analysis identified age (Hazard-ratio [HR]= 1.03, 95% confidence interval (CI): 1–1.08, p=0.02), heart failure (HR= 1.9, 95%CI: 1.3–3, p= 0.0018), and LVEF (HR= 1.04, 95%CI: 1.01–1.07, p=0.0253) as independent predictors of long-term mortality. Furthermore, MVR was not associated with worse long-term survival on both univariate (p=0.83) and multivariate (p=0.98) analysis. Performing mitral valve surgery is safe in patients with severe OMR and no or mild symptoms. Impaired LVEF is associated with increased short- and long-term mortality, suggesting that these patients should be promptly operated before the onset of LV dysfunction.