Balloon dilation of recoarctation of the aorta was performed 47 times in 44 patients 49 +/- 54 months after surgical repair. The initial operation was performed in the neonatal period in 29 patients (66%). The age at balloon dilation was 4.9 +/- 5.3 years (range 2 months to 20 years) and weight was 18 +/- 15 kg (range 2 to 72). Systolic pressure difference across the recoarctation site decreased from 37 +/- 16 to 14 +/- 11 mm Hg and coarctation/aortic diameter ratio increased from 0.45 +/- 0.14 to 0.85 +/- 0.16 immediately after balloon dilation regardless of the nature of the previous operation (subclavian flap [n = 12], resection with end to end anastomosis [n = 21], patch angioplasty [n = 4] or multiple operations [n = 5]). In the ascending aorta, systolic pressure decreased from 120 +/- 25 to 113 +/- 20 mm Hg. In the descending aorta, systolic pressure increased from 85 +/- 15 to 100 +/- 19 mm Hg and pulse pressure increased from 22 +/- 7 to 36 +/- 8 mm Hg. At repeat cardiac catheterization in 21 patients (48%) 12 +/- 8 months after balloon dilation, there was further reduction in systolic pressure difference from 17 +/- 11 to 12 +/- 9 mm Hg with no further change in coarctation/aortic diameter ratio. Aneurysm formation was evident in one patient (2%) immediately after balloon dilation; the aneurysm was unchanged at repeat study 15 months later. A "new" aneurysm was apparent in 2 (10%) of the other 20 patients restudied to date. The occurrence of aneurysm in these three patients was unrelated to balloon size. There were no procedure-related deaths. Three patients (7%) had femoral artery occlusion. Balloon dilation affords good relief of obstruction without adverse sequelae from aortic wall disruption at medium-term follow-up.