AIMS: Mitral valve prolapse is a common source of severe mitral regurgitation in Western countries. Three-dimensional echocardiography can provide views of the entire valve, allowing a complete assessment of the valve leaflets and commissures. It has the potential to precisely locate and quantify mitral valve prolapse. METHODS AND RESULTS: Between January 1997 and December 2000, 91 patients with severe mitral regurgitation due to mitral valve prolapse underwent a transesophageal echocardiography with three-dimensional reconstruction of the mitral valve as part of their pre-operative work-up. The location and extent of the prolapse by echo was compared to the surgical status. The volume of prolapsing leaflet was calculated and compared to the volume of resected tissue whenever a repair was attempted. There was an excellent correspondence between the echographic localization of the prolapse and surgical inspection, and between the volume of prolapsing and surgically resected tissue (r=0.94, p<0.0001). CONCLUSIONS: In patients with severe mitral regurgitation due to mitral valve prolapse, 3D echo allowed a precise localization and an accurate quantification of the prolapsing portion of the leaflets. This technique can provide refinements in the surgical planning of mitral valve repair and in the selection of candidates for this intervention.