M-mode echocardiograms of six patients with a diagnosis of Ebstein's anomaly and confirmed by cardiac catheterization were reviewed. All the patients (5 females and 1 male) were Caucasians with their ages ranging from one day to twenty-six years. The tricuspid valve was easily located in all the echo cardiographic studies. There was a 45 to 100 msec delay in tricuspid valve closure as compared to the mitral valve closure, in all patients. The amplitude of the anterior tricuspid valve was found to be greater than the amplitude of the anterior mitral valve in all but one case. Paradoxical septal movement type A was observed in four cases. None of the cases had a right ventricular end diastolic diameter that was larger than the left ventricular end diastolic diameter. The study found that it was extremely difficult to specifically diagnose Ebstein's anomaly with M-mode echocardiography alone, as each case has not been able to meet with all the criteria for diagnosis, described by various investigators.