In 14 consecutive 9- to 18-year-old patients with preductal aortic coarctation and isthmic hypoplasia, we resected the coarctation ridge through a longitudinal aortotomy and widened the aorta with an in situ left internal mammary artery flap. This technique resulted in no surgical complications. At 6-month follow-up examination, the average decrease in systolic pressure across the repair was 8.8 mmHg; all patients showed a clear reduction in arterial hypertension at rest and during exercise. Femoral pulses were easily palpable in all cases. Angiography and magnetic resonance imaging showed no aneurysm formation. The narrowest internal diameter of repair was 88% +/- 12% (mean +/- SD) of the diameter of the aortic arch. The internal mammary artery flap technique, which reflects the basic principle of autogenous arterial grafting in situ, allows appropriate circumferential widening of the aorta in many patients with coarctation and hypoplasia of the aortic isthmus involving delayed repair. This procedure should be considered when the internal mammary artery is of good caliber and quality and the anatomic conditions are not ideal for classic end-to-end anastomotic repair.