Between May 1985 and April 1991, 30 patients (seven females and 23 males) 14 to 54 years old (median, 25 years) underwent balloon angioplasty for unoperated native (n = 26) or recurrent postoperative (n = 4) coarctation of the aorta. 28/30 patients had systemic hypertension (RR > 140/90 mmHg). Dilatation of the stenotic segment could be achieved in 28/30 patients. The residual pressure gradient was > 30 mmHg in six patients. In 2/4 patients with recurrent coarctation the balloon had ruptured, while dilatation was successful in the other two patients. The mean diameter of the stenotic segment increased from 5.8 +/- 2.7 mm to 11.9 +/- 2.5 mm and the peak pressure gradient decreased from 61 +/- 18 mmHg to 20 +/- 13 mmHg. Complications were a small hemorrhagic pleural effusion in one patient and a groin hematoma in another patient. Clinical follow-up studies with retrograde catheterization of the aorta and angiography were performed in all 28 patients with dilated coarctation, 6 months to 6 years after the procedure, representing a total follow-up time of 72 (average, 2.6) patient-years. Multiple follow-up studies (n = 2-4) were performed in 17/28 patients. In one patient the first angiogram revealed aneurysm formation while a small bulge was seen in two others. Intra-aortic pressure measurements revealed a peak gradient of < 30 mmHg in 24/28 patients with a mean of 14 +/- 10 mmHg. The blood pressure was normal in 23/28 patients. In the other five patients whose pressure gradients were 7, 30, 30, 35, and 60 mmHg moderate hypertension persisted.(ABSTRACT TRUNCATED AT 250 WORDS)