Although balloon aortic valvuloplasty (BAV) is effective in the acute management of valvar aortic stenosis (AS), sustained benefit of this technique has been shown to vary in differing age groups. The role of BAV in the young adult with congenital, nondegenerative AS is poorly defined. The catheterization results and follow-up echocardiographic data were reviewed for all patients (n = 18) between the ages of 17 and 40 years (mean 23 +/- 7) undergoing BAV at our institution between March 1986 and January 1992. Peak-to-peak systolic ejection gradient was reduced by 55%, from 85 +/- 29 to 38 +/- 17 mm Hg (p < 0.001). Aortic valve area increased from 0.9 +/- 0.2 to 1.1 +/- 0.3 cm2 (p = 0.003). Results of dilation were inadequate in 2 patients. There were no deaths, myocardial infarction, or embolic events. The 16 "effectively" dilated patients were followed with serial echocardiography for a period of 1 to 82 months, demonstrating persistent gradient relief in most patients (maximal instantaneous gradient at follow-up, 55 +/- 17 vs 79 +/- 22 mm Hg before dilation, p < 0.001). Aortic valve replacements were performed in 5 patients, 2 with unsuccessful initial dilations. At the time of the most recent echocardiogram, 8 of 16 patients remained "incident free," with no subsequent catheterization or surgical interventions, a maximal instantaneous gradient of < or = 55 mm Hg, no more than moderate aortic regurgitation, and preserved ventricular function.(ABSTRACT TRUNCATED AT 250 WORDS)