Smaller patient series have not explored the independent relations between patient selection and technical factors that may impact on acute results of percutaneous balloon aortic valvotomy. To determine such relations, results from the Valvuloplasty and Angioplasty of Congenital Anomalies Registry were examined from 630 balloon aortic valvotomies in 606 patients from 23 institutions. Median age was 6.8 years (range 1 day to 18 years). The procedure could not be performed or completed in 4.1%. The left ventricular to aortic gradient was reduced by a mean +/- SD of 60 +/- 23% (p < 0.0001). Procedure-related mortality was 1.9%. A suboptimal outcome was defined arbitrarily as failure to perform the procedure, a residual gradient > or = 60 mm Hg or LV: aortic pressure ratio > or = 1.6, or major morbidity or mortality, and was noted for 17% of procedures. Independent risk factors from multiple logistic regression analyses included age < 3 months, higher preprocedure gradient, earlier procedure date, the presence of unrepaired aortic coarctation, and the use of undersized balloons. Detailed analysis revealed the optimal balloon: valve diameter ratio to be 0.9 to 1.0, with undersized balloons resulting in significant residual obstruction and oversized balloons resulting in aortic regurgitation complications. Improvements in results over time were related to increasing experience within individual institutions. Thus, percutaneous balloon aortic valvotomy provides adequate relief of obstruction, with minimal complications in most patients.