Mitral valve (MV) repair is the procedure of choice for MV prolapse or flail. However, valve repair is more technically demanding and requires a precise definition of MV morphology to determine the timing, complexity, and feasibility of repair. We prospectively examined 170 consecutive patients with MV prolapse or flail referred for MV repair. The MV valve was systematically assessed by intraoperative transesophageal echocardiography. MV anatomy was independently assessed at the time of operation. Accuracy of transesophageal echocardiography in identifying MV segments ranged from 90% to 97%, and was best for the middle segment/scallop of either anterior or posterior leaflet. MV repair was successful in 91% of patients. Success rate was the lowest (78%) in the presence of extensive bileaflet disease involving at least 2 segments of each leaflet. Independent predictors of unsuccessful repair were central jet of mitral regurgitation, calcification or severe dilatation of the mitral annulus, and extensive leaflet disease with involvement of at least 3 segments.