Background: Mitral valve (MV) coaptation is very important in MV repair patients. But accurate quantitation of the degree of MV coaptation remains challenging. This study aimed to evaluate the utility of two-dimensional (2D) and three-dimensional (3D) transesophageal echocardiography (TEE) to assess MV coaptation before and after MV repair. Methods: Forty-eight patients [(age: 52.23 +/- 13.31 years; 26 men (54.17%)] undergoing MV repair for mitral regurgitation (MR) were studied. We assessed the utility of 2D and 3D TEE to assess MV coaptation before and after MV repair. Complete conventional 2D and 3D TEE studies were performed, and the degree of the MV coaptation defect before and after surgery was assessed by measuring the MV coaptation length (CL) and length index (CLI) with 2D TEE, and the coaptation area (CA) and coaptation area index (CAI) with 3D TEE. Results: CL and CLI were measured successfully in 46 (95.83%) patients and CA and CAI in 39 (81.25%). Compared with preoperatively, postoperative CL, CLI, CA, and CAI were significantly increased (CL: 4.99 +/- 0.79 to 9.66 +/- 1.09 mm, P<0.05; CLI: 9.30%+/- 2.66% to 38.24%+/- 3.82%, P<0.05; CA: 158.49 +/- 64.17 to 371.33 +/- 143.57 mm(2), P<0.05; CAI: 9.71%+/- 2.76% to 36.24%+/- 7.26%, P<0.05). Spearman's rank correlation analysis revealed that the CLI and CAI had a significant negative correlation with the degree of MR (r=-0.97, P<0.01; r=-0.92, P<0.01, respectively). Furthermore, Pearson's correlation analysis revealed that the CLI was significantly correlated with the CAI both preoperatively (r=-0.66, P<0.01) and postoperatively (r=-0.67, P<0.01). Conclusions: The coaptation variables increased significantly in patients undergoing MV repair. The CLI and CAI significantly correlated with MR severity. The CL and CLI determined with 2D TEE are more feasible than the CA and CAI determined with 3D TEE. Both 2D and 3D variables may complement each other for aiding MV repair. 2D CLI is an alternative to 3D CAI due to its simplicity.