Membranous obstruction of upper cava is one of the frequent causes of inferior vena caval obstruction in this country. Since it can be cured by transcardiac membranotomy or other interventions, accurate diagnosis of the disease is important. Sonographic findings in 6 cases of membranous obstruction of inferior vena cava were analysed and correlated with the findings of the inferior venacavography. At the obstructed site, the membrane was detected as a high echogenic focal or segmental obliteration of the lumen sonographically. The lumen of vena cava below the obstruction was easily delineated without normal respiratory changes. Venacavography was superior in demonstrating all collateral channels except transhepatic collaterals which were depicted well in sonography.