Patch aortoplasty relieves the aortic pressure gradient substantially better than resection with end-to-end anastomosis in infants with coarctation of the aorta. Growth of the intact posterior wall of the unresected coarctation after aortoplasty, however, has not yet been demonstrated to occur. Infants (21) < 2 yr of age who underwent prosthetic patch repair of coarctation after 1975 were studied. Associated lesions were present in 16 patients, and 12 had a concomitant procedure. Two patients died in the hospital, and 4 died later, all of causes unrelated to the coarctation repair. Systolic blood pressure in the right arm declined from 140 .+-. 41 mm Hg (mean .+-. SD) preoperatively to 101 .+-. 19 mm Hg postoperatively in the whole group and to 95 .+-. 12 in 10 patients followed for > 3 yr. The right arm-left leg systolic pressure gradient declined from 66 .+-. 22 mm Hg to 5 .+-. 14 in all patients and 4 .+-. 13 in the group followed > 3 yr. Hypoplastic transverse arch was seen in all but 2 patients. Its relative diameter increased in 6 of 9 patients who underwent catheterization postoperatively and increased > 50% in 3 patients. Two patients have evidence of narrowing of the aorta at the patch, but both have normal blood pressure in the right arm. In the patient with longest follow-up (an 8-mo.-old infant seen 8 yr after operation) angiograms show the diameter of the aorta at the coarctation to be greater than that at the transverse arch and at the descending aorta. Hemodynamic and angiographic results up to 8 yr after patch repair remain good, and there is evidence that both the hypoplastic and intact posterior wall of the aorta can grow after patch repair of coarctation in infancy.