To evaluate the diagnostic accuracy of two-dimensional echocardiogrphy(2-D echo) in ventricular septal defect, location and size of the defects, estimated right ventricular systolic pressure and associated cardiac anomaly were compared to the operative findings in 139 children operated for correction of ventricular septal defect at Severance Hospital from Jan. 1983 to June 1987. In addition, postoperative complications and mortality cases were anlysed. The following results were obtained; 1) Perimembranous defects were 82 cases(66.1%), subarterial infundibular defects 33 cases(26.6%), and muscular defect was found in only 1 case(0.8%). The accuracy of 2-D echo in localizing the defects was 84.2%. 2) In 79.2% of the patients, the defects were moderate to large in size, and actual size measured at operation was larger than that obtained by echocardography in general. 3) The estimated right ventricular systolic pressure was correlated(r=0.650) with that measured at the operating field. 4) Combined cardiac anomalies were patent ductus arteriosus(22 cases), atrial septal defect(3 cases), valvular pulmonic stenosis(2 cases) and interventricular septal aneurysm(2 cases). The sensitivity of 2-D echo in detecting these anomalies was 65.5% and the specificity was 96.4%. 5) Among 32 patients who had postoperative complications, in two thirds, there were pulmonary complication including lung atelectasis(16 cases), pleural effusion(5 cases)and pneumonia(5 cases). 6) Operative mortality was 2.9%(4 cases). The causes of death were low cardiac output state due to left ventricular myocardial failure in 3 patients and respiratory failure from asphyxia in one case. In conclusion, with close cooperation with cardiac surgeons, there will be few problems in diagnosing and operating patients with ventricular septal defect on the basis of two-dimensional echocardiographic findings without invasive procedures, such as cardiac catheterization, even with pulmonary hypertension, unless Eisenmenger syndrome is complicated.