Background: Mitral valve (MV) repair is preferred over replacement in clinical guidelines and is an important determinant of the indication for surgery in degenerative mitral regurgitation. However, the level of evidence supporting current recommendations is low, and recent data cast doubts on its validity in the current era. Accordingly, the aim of the present study was to analyze very long-term outcome after MV repair and replacement for degenerative mitral regurgitation with a flail leaflet. Methods: MIDA (Mitral Regurgitation International Database) is a multicenter registry enrolling patients with degenerative mitral regurgitation with a flail leaflet in 6 tertiary European and US centers. We analyzed the outcome after MV repair (n=1709) and replacement (n=213) overall, by propensity score matching, and by inverse probability-of-treatment weighting. Results: At baseline, patients undergoing MV repair were younger, had more comorbidities, and were more likely to present with a posterior leaflet prolapse than those undergoing MV replacement. After propensity score matching and inverse probability-of-treatment weighting, the 2 treatments groups were balanced, and absolute standardized differences were usually P P P P P Conclusions: Among patients with degenerative mitral regurgitation with a flail leaflet referred to mitral surgery, MV repair was associated with lower operative mortality, better long-term survival, and fewer valve-related complications compared with MV replacement.