The purpose of this study was to report on 3- to 9-year follow-up data after balloon aortic valvuloplasty in children and to investigate causes of aortic insufficiency at late follow-up. Although the immediate and short-term results of balloon aortic valvuloplasty have been well documented, little information is available on long-term follow-up results. During a 7.3-year period ending December 1992, 26 young patients, aged 6 weeks to 20 years, underwent balloon aortic valvuloplasty with resultant reduction of peak-to-peak aortic valvar gradient from 71 +/- 20 (mean +/- SD) to 25 +/- 12 mm Hg (p < 0.001). None required immediate surgical intervention. At intermediate-term follow-up, 6 (23%) of 26 had restenosis develop and underwent surgical (4 patients) or repeat balloon valvuloplasty (2 patients). Clinical and echo-Doppler data 3 to 9 years (median 6 years) after balloon valvuloplasty revealed residual peak instantaneous Doppler gradients of 26 +/- 13 mm Hg (p < 0.001), without restenosis beyond what was observed at intermediate-term follow-up. Aortic insufficiency progressed in seven patients. However, none required intervention. Actuarial intervention-free rates at 1, 2, 5, and 9 years were 80%, 76%, 76%, and 76%, respectively. Logistic regression analysis suggested that the degree of Doppler-quantitated aortic insufficiency 1 day after valvuloplasty predicts persistent aortic insufficiency at late follow-up. These data indicate that immediately successful balloon aortic valvuloplasty in children yields a residual gradient of < or = 36 mm Hg at a median of 6 years of follow-up in most patients and an intervention-free rate at 9 years of 76%. Restenosis occurs but can be treated with a repeat intervention with good results. Aortic insufficiency remains stable and does not appear to require intervention, at least during the first decade after balloon dilatation.