Thirty patients operated on for aortic coarctation while less than 3 years of age underwent magnetic resonance imaging, digital subtraction angiography, and bicycle exercise testing 14 to 33 years (mean, 22 years) after operation. Diameters of the aorta at the site of the anastomosis, of the distal arch, and of the aorta at the level of the diaphragm were measured in the images. Blood pressures were obtained from the right arm and leg before and after exercise. Patients were divided into three groups according to blood pressure data: group I, resting gradient less than 30 mm Hg and exercise gradient less than 50 mm Hg; group II, resting gradient less than 30 mm Hg and exercise gradient greater than 50 mm Hg; and group III, resting gradient 30 mm Hg or greater. A control group underwent the same test. The frequency of hypertensive patients was greater in groups II (58%) and III (100%) than in group I (20%). The anastomosis/descending aorta ratio seen in digital subtraction angiograms was smaller in group II and III patients. Exercise blood pressure gradient correlated significantly (r = -0.48; p = 0.009) with anastomosis/descending aorta ratio in digital subtraction angiograms but not in magnetic resonance images. Twenty of 30 patients (67%) had a significant anatomic narrowing at the site of the anastomosis. Blood pressure data correlated with diameters measured in digital subtraction angiograms but not with diameters measured in magnetic resonance images.