Balloon dilation angioplasty was attempted in 10 infants and children with severe congenital or operative 'venous' obstructions. In five children the obstructions were 'vena caval' and followed repair for transposition of the great vessels (four patients) or orthotopic liver transplantation (one patient). In the four patients with fixed vena caval or baffle obstructions, balloon angioplasty was successful in relieving the obstruction, decreasing the average gradient (16.0 to 4.5 mm Hg), and increasing the average diameter (3.0 to 8.9 mm) of the obstructed site. One child died 1 week later from an unrelated cerebral hemorrhage; the three survivors have had persistent clinical and angiographic improvement. The fifth child had severe systolic narrowing of the superior baffle limb caused by marked tricuspid regurgitation, which ballooned the superior limb of the baffle against the atrial roof. Angioplasty was unsuccessful in relieving this type of obstruction, which resolved with tricuspid valve replacement. Of the five infants with obstructed pulmonary veins, three had congenitally narrowed vessels associated with total anomalous pulmonary venous connection, one had acquired stenosis, and one had postoperative obstruction after repair of a mixed type of total anomalous pulmonary venous connection. Dilation was unsuccessful in all five patients, but for different reasons: in the congenitally narrowed veins, the waist in the balloon could not be eliminated, even with high dilating pressures; in the infant with acquired stenosis, the vein stretched but did not tear at low dilating pressures; and in the postoperative obstruction, angioplasty increased the diameter of the obstruction but did not increase flow to the affected lung. Venous obstructions in children are heterogenous lesions, and the success of angioplasty in relieving such obstructions will depend not only on the technique used but also on the nature of the obstruction.