The reliability of biplane transesophageal color Doppler echocardiography for the evaluation of mitral valve prolapse was assessed by comparison with surgical findings in 27 patients. The mitral valve prolapse site was classified as the medial, central, and lateral portions of the anterior leaflet, and medial, middle, and lateral scallops of the posterior leaflet. The prolapsed sites were determined by the site of systolic displacement using two-dimensional echocardiography, the site of flow acceleration and the direction of the mitral regurgitant jet using color Doppler echocardiography. The sensitivity of transesophageal echocardiography for detecting prolapse at the medial, central, and lateral portions of the anterior leaflet, and the medial, middle and lateral scallops of the posterior leaflet was 91, 100, 86, 83, 100, and 80%, respectively. The specificity was 100, 100, 96, 100, 89, and 100%, respectively. Biplane transesophageal echocardiography is a reliable method for detecting the site of mitral valve prolapse.