To assess the accuracy of 2-dimensional (2-D) echocardiography in the evaluation of cardiac anatomy in patients with congenital heart disease, 2-D echocardiograms were performed in 126 infants and children before cardiac catheterization and angiocardiography. The segmental echocardiographic analysis included determination of intracardiac, great artery, systemic venous and pulmonary venous anatomy. The 126 patients had 259 separate cardiovascular abnormalities, of which 226 (87%) were prospectively identified by 2-D echocardiography. There were 8 false-positive diagnoses. The most common lesions and the sensitivity and specificity of echocardiography were: patent ductus arteriosus, 41 patients (83% and 100%, respectively), ventricular septal defect, 35 patients (86% and 100%); atrial septal defect, 26 patients (85% and 99%); pulmonary valve stenosis, 25 patients (77% and 97%), transposition of the great arteries, 16 patients (100% and 100%); and total anomalous pulmonary venous connection, 14 patients (85% and 100%). Less common defects and their rate of detection included coarctation of the aorta, 10 of 12 patients; atrioventricular canal, 10 of 10 patients; tetralogy of Fallot, 10 of 10 patients; aortic valve stenosis 8 of 8 patients; right aortic arch, 8 of 8 patients; interrupted aortic arch, 4 of 4 patients; and unilateral pulmonary vein atresia, 0 of 1 patient. In 33 patients (26%), the errors in echocardiographic analysis were judged to have surgical importance. Most errors were the result of overlooking or misinterpreting data that had been appropriately recorded on videotape. Pulmonary valve stenosis and patent ductus arteriosus are the lesions most likely to be misdiagnosed by ultrasound studies relying on imaging alone.