BACKGROUND Two-dimensional transesophageal echocardiography (2D TEE) Doppler color flow imaging is the gold standard for assessing the severity of mitral regurgitation (MR). Severe MR with very eccentric jet may involve more than one mitral leaflet lesion and can be missed by 2D TEE. The purpose of this study was to assess the usefulness and the incremental value of real-time three-dimensional (RT 3D) TEE over 2D TEE findings in the evaluation of patients suffering eccentric MR with more than one mitral leaflet lesion. METHODS Intraoperative 2D TEE and RT 3D TEE examinations were performed on 168 patients with Carpenter II MR who underwent surgery. MR was defined as either central, free-standing eccentric jet or very eccentric jet. 2D TEE and RT 3D TEE finding were compared with surgical findings. RESULTS Of these 168 MR patients, 25 patients (14.9%) had central jets and 143 patients (85.1%) had eccentric jets. Among 143 patients with eccentric jets, 47 patients (32.9%) had free-standing eccentric MR jets, and 96 (67.1%) patients had very eccentric jets. 3D TEE diagnosed the severity and location of MR lesions correctly in all patients; this was not the case with 2D TEE, which had significant diagnostic misses in nine patients (9.4%, p < 0.001) having MR with very eccentric jets. These nine patients had lesions on both mitral leaflets, which were missed during 2D TEE examination owing to the highly turbulent flows produced by very eccentric jets from one mitral leaflet lesion and impinging the opposite mitral leaflet lesion. CONCLUSIONS The severity of MR with very eccentric jet was more accurately and comprehensively assessed by 3D TEE than by 2D TEE. Therefore, intraoperative RT 3D TEE provides incremental information that is generally superior to 2D TEE in patients with complex MR due to very eccentric jets.