Background: As mortality of patients with severe mitral regurgitation (MR) due to prolapse or flail leaflet has been reported unacceptably high, clinical outcomes of watchful waiting needs to be reevaluated. Methods and Results: A total of 506 patients with degenerative MR (age 47짹16 years; 53% male) was prospectively enrolled and follow-up (F/U) was done until April 2009. Surgical timing was determined using the established guideline including left ventricular dimension, ejection fraction, and development of symptoms or pulmonary hypertension. Comprehensive echo-Doppler examination showed 337 patients with severe MR (67%, group I) and 169 with mild or moderate MR (group II). During clinical F/U of 4.7짹3.4 years, MR surgery was done in 213 patients (42%). All cause of mortality and cardiovascular (CV) mortality developed in 26 (5.1%) and 14 (2.8%), respectively. In group I, CV death included 3 operative mortality (0.6%) with 1 unexpected sudden death and 1 fatal infective endocarditis. Three patients died of heart failure after refusal of elective surgery. In group II, recurrent pneumonia (n=2), infective endocarditis (n=1), and old age (>80 years) with pulmonary hypertension (n=2) were associated with CV death. Although overall survival rate tended to be lower in group I (p=0.06), CV death-free survival did not differ between groups (p=0.99). Multivariate analysis showed age was the only factor associated with CV mortality (hazard ratio, 2.0 per 10 years; 95% confidence intervals, 1.5 to 2.9, p=0.001). Conclusions: In patients with degenerative MR, CV mortality rate is low with watchful waiting and strict application of the current established guideline for surgical timing.