Oversized dilatation balloons are recommended for relief of valvar pulmonic stenosis in infants and children during cardiac catheterization. Little information exists about the long‐term outcome of this practice. Six of 107 consecutive patients undergoing balloon pulmonary valveplasty developed increasing pulmonary valve incompetence during follow‐up periods of 0.5–10 years (mean, 7.2 years). Secondary right ventricular dilatation prompted insertion of a bioprosthetic pulmonary valve in one patient 6.8 years after intervention; valve replacement is pending in two additional patients, 4.3 and 10 years after intervention, respectively; and the three remaining subjects are thought likely to require valve replacement during childhood. The six reported subjects differ from the pulmonary valveplasty group as a whole in that they are younger (median age, 3 days vs. 11 months), had a higher degree of obstruction (right/left ventricular systolic pressure ratio prior to valveplasty 1.28 vs. 0.92), and underwent dilatation with relatively oversized balloons (balloon diameter to pulmonary valve annulus ratio 1.44 vs. 1.08). The balloon diameter to valve annulus ratio did not exceed 1.5 in any subject. Caution is advised in the use of oversized dilatation balloons in neonates or young infants with severe or critical pulmonic stenosis. Long‐term consequences of substantial pulmonary valve incompetence outweigh, in our opinion, the limited gradient relief achieved with smaller balloons, sometimes requiring a second dilatation of the valve at an older age and larger size. Cathet. Cardiovasc. Intervent. 48:61–65, 1999. © 1999 Wiley‐Liss, Inc.