We compared live/real time three-dimensional transesophageal echocardiography (3D TEE) with real time two-dimensional transesophageal echocardiography (2D TEE) in the assessment of individual mitral valve (MV) segment/scallop prolapse and associated chordae rupture in 18 adult patients with a flail MV undergoing surgery for mitral regurgitation. 2D TEE was able to diagnose the prolapsing segment/scallop and associated chordae rupture correctly in only 9 of 18 patients when compared to surgery. In three of these, 2D TEE diagnosed an additional segment/scallop not confirmed at surgery. In the remaining nine patients, surgical findings were missed by 2D TEE. On the other hand with 3D TEE, the prolapsed segment/scallop and associated ruptured chords correlated exactly with the surgical findings in the operating room in 16 of 18 patients. The exceptions were two patients. In one, 3D TEE diagnosed prolapse and ruptured chordae of the A3 segment and P3 scallop, while the surgical finding was chordae rupture of the A3 segment but only prolapse without chordae rupture of the P3 scallop. In the other patient, 3D TEE diagnosed prolapse and chordae rupture of P1 scallop and prolapse without chordae rupture of the A1 and A2 segments, while at surgery chordae rupture involved A1, A2, and P1. This preliminary study demonstrates the superiority of 3D TEE over 2D TEE in the evaluation of individual MV segment/scallop prolapse and associated ruptured chordae.