The reported incidence of aortic aneurysm after surgical repair or balloon angioplasty for aortic coarctation varies widely. To determine the incidence of aneurysm formation after surgery, preoperative and postoperative cineangiograms from 65 patients who underwent operation at age 1.5 +/- 3.4 years were examined. Repair included a prosthetic patch in 14 patients, end to end anastomosis in 28 and subclavian flap in 23. Aneurysm was documented by change in contour or irregularities in contour at the repair site or by abnormal dimensions at the repair site, defined by the ratio of the widest measurement at the repair site to the measurement of the aorta at the diaphragm. An aneurysmal bulge above the ductus diverticulum was identified in 14 (23%) of 60 patients preoperatively; the area showed no change 4.72 +/- 4.07 years after surgery. Significant changes at the repair site were seen in only three patients, all of whom had Dacron patch repair. One patient had a change in contour at the repair site, one had an abnormally high repair site to diaphragmatic aorta ratio and one had a progressive increase in this ratio. Thus, during childhood years, 3 (5%) of 65 patients were diagnosed as having aneurysm at the surgical repair site. In conclusion, 1) comparison with preoperative cineangiograms, especially for aneurysmal bulges above the ductus arteriosus, is essential before an aneurysm can be attributed to coarctation repair by any technique, and 2) aneurysm developed only in patients subjected to Dacron patch repair.