To evaluate the usefulness of dynamic 3-dimensional images obtained by multiplane transesophageal echocardiography (TEE) in the diagnosis of the involved leaflets in patients with a flail mitral leaflet, 23 patients who underwent mitral valve repair were examined with multiplane TEE. In all patients, the involved lesions diagnosed by dynamic 3-dimensional images coincided with those confirmed at the time of operation; dynamic 3-dimensional images by multiplane transesophageal probe are useful in the evaluation of the involved sites in patients with a flail mitral leaflet.