Objective : Mitral valve repair is the procedure of choice for mitral regurgitation of any etiology, but the failure of repair and subsequent reoperation are one of the most important problems. This study was undertaken to determine the causes of recurred mitral valve regurgitation after mitral valve repair in various etiologies. Materials and Method : We researched the effects of the etiology of mitral regurgitation and operation method on the occurrences of III/IV mitral regurgitation after surgery and reoperations in 493 patients who received mitral valve repair from Jan. 1994 to Jan. 2002. The etiology of mitral regurgitation was degenerative in 252 cases(51.5%), rheumatic in 156(31.6%), ischemic in 28(5.7%), endocarditis in 26(5.3%), congenital in 23(4.7%), myxomatous in 7(1.4%), and iatrogenic in 1. In terms of operation method, 446 ring annuloplasties(90.5%), 227 new chodae formations(46%), 125 Q-resections(25.3%), 28 chodae transfers(5.7%), and 8 Alfieri���s stitches(1.6%) was done for this group of patients. Result : Mean follow up was 29.04 짹 22.81 months. There was 5 early deaths, and 5 late deaths(1.01%). Reoperation rate was 1.42%. In 45 (9.1%) patients, III/IV mitral regurgitation was occurred after mitral valve repair. In detail, 24 procedure related recurrences were detected : 14 incomplete repair, 8 too short or too long new chodae, 1 ring dehiscence, 1 leaflet perforation. Twenty one valve related recurrences were consisted of 10 cases of progression of rheumatic diseases, 5 recurrent chodae elongation or prolapse, 3 incomplete coaptations for dilation of the heart, 2 commissural regurgitations, 1 recurred endocarditis. The occurrence of significant mitral regurgitation was significantly increased after incomplete repair(p<0.001), and disease progression had strong correlation with recurred mitral regurgitation in rheumatic group(p<0.005) Conclusion : Because incomplete initial operation was most important risk factor of recurred significant mitral regurgitation, intraoperative transesophageal echcardiographic evaluation was crucial for improving results. In rheumatic etiology, disease progression was more important cause of failed mitral valve repair than surgical procedure itself.