We evaluated the potential advantage of real-time 3-dimensional echocardiography on the assessment of mitral valve morphology and function in patients with isolated cleft mitral valve. Five patients, aged 33 +/- 9 years, with isolated cleft mitral valve and no associated cardiac anomalies, were studied. Real-time 3-dimensional echocardiography demonstrated the cleft in each case and allowed the measurement of its width and depth, the extent of cleft edge fibrosis and retraction, and the presence of accessory chordae and their attachment to the septum. Four patients had moderate or severe mitral regurgitation and in one patient the regurgitation was mild. In all patients the mitral regurgitant jet originating from the cleft was detected, and in one patient, a second jet was detected and not seen in the 2-dimensional study. Real-time 3-dimensional echocardiography is a reliable and reproducible technique that provides accurate and detailed echocardiographic characterization of the isolated cleft mitral valve in adults.