Balloon coarctation angioplasty (BCA) was performed in seven consecutive patients (five boys and two girls) 18 months to 18 years old (mean 9.5) with isolated discrete unoperated coarctation of the aorta. A No. 8F or 9F catheter was chosen with balloon lengths of 30 or 40 mm and maximum inflation diameters 1 mm less than the smallest measured aortic diameter determined 1 cm proximal to the coarctation site. A 10 sec inflation-deflation cycle of 6 to 8 atmospheres (90 to 120 psi) was performed. The peak systolic pressure gradient (PSG) before BCA ranged from 35 to 70 mm Hg (mean 58), and immediately after BCA it decreased to 0 to 20 mm Hg (mean 7). One to two year follow-up (mean 14 months) of the seven patients revealed a PSG range of 10 to 30 mm Hg (mean 19). Repeat angiography was performed immediately proximal to the coarctation site. Three patients (43%) had evidence of aneurysm formation at or immediately distal to the balloon dilatation site. One patient had coarctation restenosis. While initial results with BCA for unoperated coarctation were encouraging, current data raise serious concerns about its long-term safety and efficacy.