From 1986 to 1988, balloon aortic valvuloplasty was performed in 32 patients with congenital valvular aortic stenosis. The patients ranged in age from 2 days to 28 years (mean +/- SD 8.3 +/- 5.9). One balloon was used in 17 patients and two balloons were used in 15 patients. Immediately after valvuloplasty, peak systolic pressure gradient across the aortic valve decreased significantly from 77 +/- 27 to 23 +/- 16 mm Hg (p less than 0.01), a 70% reduction in gradient. At early follow-up study (4.1 +/- 3.3 months after valvuloplasty), there was a 48 +/- 20.5% reduction in gradient compared with that before valvuloplasty, and at late follow-up evaluation (19.2 +/- 5.6 months), a reduction in gradient of 40 +/- 29% persisted. Echocardiography showed evidence of significantly increased aortic regurgitation in 10 patients (31%) and aortic valve prolapse in 7 patients (22%). There was no correlation between the balloon/anulus ratio and the subsequent development of aortic regurgitation or prolapse. In fact, no patient who showed a significant increase in aortic regurgitation had had a balloon/anulus ratio greater than 100%. It is concluded that balloon aortic valvuloplasty effectively reduces peak systolic pressure gradient across the aortic valve in patients with congenital aortic stenosis. However, subsequent aortic regurgitation and prolapse occur in a significant number of patients, even if appropriate technique and a balloon size no greater than that of the aortic anulus are used.