This prospective study was conducted to ascertain whether echocardiographic evaluation could provide more insight into the genesis of mitral regurgitation (MR) before surgery. All patients underwent preoperative transthoracic and transesophageal echocardiography. Nine centers participated in the ESMIR (Echocardiographic Selection of patients for MItral valve Reconstruction) study and 350 patients were included. Compared with surgical findings, the percentage of functional abnormalities correctly predicted by both echo modalities was highest in patients with increased leaflet mobility (83% for transthoracic and 86% transesophageal echocardiography). In contrast, in normal leaflet mobility, the prediction was better by transthoracic than by transesophageal echocardiography (75% vs 64%). In patients with restricted leaflet mobility, the predictive value of both techniques was similar. The diagnostic yield of anatomic abnormalities of both echo techniques was similar, except for chordal rupture; a sensitivity by transesophageal echocardiography of 79% and by transthoracic echocardiography of 57% (p < 0.001). In general, the sensitivity of each echo technique for detecting anatomic abnormalities was <70%, except for annular dilatation, leaflet thickening, and chordal rupture. At surgery, the prevailing functional condition was increased leaflet mobility (42%). The conclusion is that both echo techniques provide adequate information regarding the functional condition of the mitral valve apparatus, not withstanding limitations in assessing anatomic details. Transthoracic echocardiography appears to be sufficient for preoperative evaluation of MR.