The purpose of this study was to determine the most discriminating clinical and echocardiographic features that are most helpful in correctly identifying Ebstein's anomaly of the tricuspid valve from other causes of tricuspid regurgitation. Ebstein's anomaly is an uncommon malformation of the tricuspid valve with diagnostic echocardiographic features. Other cardiac disorders associated with tricuspid valve regurgitation and predominate right-sided heart chamber enlargement can be misdiagnosed as Ebstein's anomaly. All patients who were referred to our institution between 1982 and 1995 with the diagnosis of Ebstein's anomaly but were found to have other abnormalities of the tricuspid value or right ventricle were identified. Their clinical, echocardiographic, and surgical records were reviewed retrospectively. Twenty-two patients (12 males and 10 females), aged 7 to 68 years (mean 33 years), were referred to our institution with the diagnosis of Ebstein's anomaly but were found to have another abnormality that mimicked clinical and diagnostic features of Ebstein's anomaly. The most common initial symptom was exercise intolerance (13 [59%] patients) followed by atrial arrhythmia (seven [32%] patients). Two patients had cyanosis. Three patients had paroxysmal and six had chronic atrial fibrillation/flutter. Cardiomegaly on chest x-ray film was noted in 18 (82%) patients. Referral diagnosis of Ebstein's anomaly had been made by echocardiography (12 patients), cardiac catheterization (four patients), both techniques (five patients), and echocardiography and magnetic resonance imaging (one patient). All 22 patients had predominate right atrial and right ventricular enlargement, and 18 (82%) of 22 patients also had right ventricular dysfunction. However, Ebstein's anomaly was confidently ruled out with repeat comprehensive echocardiography at our institution by establishing (1) absence of significant apical displacement of the septal tricuspid valve leaflet (> or = 8 mm/m2) and (2) lack of a redundant, elongated, anterior tricuspid valve leaflet in all 22 patients (100%). All had significant tricuspid regurgitation caused by tricuspid valve dysplasia (nine patients), tricuspid valve prolapse (four patients), trauma (four patients), right ventricular dysplasia (three patients), endocarditis (one patient), and annular dilation caused by free pulmonary regurgitation (one patient). In all 15 patients who subsequently underwent surgery (tricuspid valve repair [seven patients] or replacement [eight patients]), the absence of Ebstein's anomaly was confirmed. Echocardiographic absence of the characteristic degree of displacement of the septal leaflet of the tricuspid valve (> or = 8 mm/m2) and the presence of a nonelongated, nonredundant anterior tricuspid valve leaflet consistently excluded the diagnosis of Ebstein's anomaly. Under such circumstances, other anomalies of the tricuspid valve or right ventricle were consistently identified. Recognition of the mimics of Ebstein's anomaly had important surgical implications.