Infrahepatic interruption of the inferior vena cava with azygos continuation is relatively infrequent cardiovascular developmental anomaly occurring both in association with congenital heart disease and as an isolated anomaly of no hemodynamic importance. During the past 5 years, we observed 38 cases of infrahepatic interruption of IVC with azygos continuation out of 2,397 cases of congenital heart disease catheterized at Yonsei Cardiovascular Center. We conducted the study with a view point of position of the heart and abdominal organs and segmental analysis of the underlying congenital heart disease. We also analysed the associated exracardiac vascular anomalies The following results wer obtained: 1) The incidence of this anomaly among congenital heart disease was 1.7% and the sex ratio 1.4:1. Twenty four cases(63.1%) was below 5 years of age and 30 cases (79.0%) had cyanosis. 2) We observed 21 cases (55.2%) with the malposition of the heart and 17 cases (44.8%) with malposition of the abdominal organs. The ventricular loops revealed D-loop in 25 cases, L-loop in 5 cases and in the remaining 7 cases, it was uncertain. Eighteen showed normally related great arteries and malposition was present in another 18 cases. 3) Associatcd cardiovascular anomalics wcre as follows: right-sidcd aortic arch: 12 cases, patentductus arteriosus: 10 cases, pulmonic stenosis: 19 cases and bilateral superior vena cava: 9 cases. In conclusion, the presence of this anomaly should alert one to seek the severeintracardiac anomalies which are usually associated with it. Also, it is essential that, if any patient with this anomaly should come to thoracotomy, the azygos vein be not sacrificed.