The clinical features and natural history of Ebstein's anomaly are analyzed on the basis of experience with 67 consecutive patients who have had a mean follow-up of 12 years. Of the total group, 26 (39%) of the patients remained in functional Class I or II and 41 (61%) progressed at some time into Class III or IV. Death occurred in 14 (21%) of the patients, and these were characterized by one or more of the following features: (1) they were in functional Class III or IV, (2) they had moderate to severe cardiomegaly with a cardiothoracic ratio greater than 0.65, (3) they had cyanosis or an arterial oxygen saturation of less than 90%, and (4) they were infants when the diagnosis was made (10 patients, of whom 5 died). In patients in Class III or IV, a comparison was made between patients treated medically (10) and those treated surgically--either with tricuspid valve replacement (15) or with a modified tricuspid annuloplasty (16). It appears that modified tricuspid annuloplasty is the procedure of choice, because despite an operative mortality of 25% (4 patients), 12 of the 16 patients so treated improved clinically or had a reduction in heart size.