Balloon angioplasty for coarctation of the aorta was performed in 45 patients; 17 (Group 1) were infants (mean age 34 +/- 43 days). This study focuses on the remaining 28 patients (Group 2), children and adults ranging in age from 2 to 31 years (mean 13 +/- 8). Two patients had had previous surgery for coarctation; in the remaining 26 the coarctation had not been surgically treated. Twenty patients (71%) had a discrete type of coarctation; the remaining eight had a diffuse or eccentric stenosis. Angiographic studies of the aorta were performed before and immediately after angioplasty in all 28 patients; 16 (57%) of them also underwent angiographic reevaluation 10 +/- 2 months later. The pressure gradient decreased immediately after angioplasty and was unchanged at follow-up. Residual gradient at follow-up ranged from 0 to 40 mm Hg (mean 11 +/- 13). Patients with a discrete type of coarctation had a lesser residual gradient than did patients with other anatomic types of coarctation. Angiographically, the stenosis also decreased after angioplasty (68 +/- 10% versus 24 +/- 17%; p less than 0.01); a new small, but significant decrease was observed at follow-up (9 +/- 18%; p less than 0.05). A quantitative analysis of the aorta at different levels revealed no significant changes proximal and distal to the coarctation segment; however, at the level of coarctation, a significant (p less than 0.01) and homogeneous increment was observed after dilation that was unchanged at follow-up. One (6%) of 16 reevaluated patients had a clear aneurysm at the site of dilation.(ABSTRACT TRUNCATED AT 250 WORDS)