Actuarial freedom from reoperation for obstruction in 147 patients receiving cryopreserved or fresh allograft valved conduits between a ventricle and the pulmonary arteries was 94% at 3.5 years. The 2 patients undergoing reoperation were 6 and 36 months of age at the time of insertion of the allograft. Among 24 patients in whom cardiac catheterization was performed on indication late postoperatively, 5 had gradients of more than 40 mm Hg across the conduit. For comparison, among 78 patients receiving xenograft or irradiated allograft valved conduits, the percentages of freedom from conduit reoperation at 3.5, 5, 10, and 15 years were 99%, 95%, 59%, and 11%, respectively. The diameters of the allograft and xenograft valves inserted varied directly with the age and size of the patients, but in patients 3 to 5 years of age, allografts with a diameter of at least 21 mm could usually be used.