The mediastinal vessels in 27 patients who had previously undergone vascular surgery were evaluated with use of magnetic resonance (MR) imaging for patency and the presence of stenosis. Thirty-six postoperative vessels or shunts were studied, including 11 aortas after coarctation or stenosis repair, 18 systemic-pulmonary shunts, four pulmonary artery or vein repairs, and three spiral vein grafts. Angiographic (n=21), direct surgical (n=1), contrast material-enhanced computed tomography (n=1), or clinical (n=13) findings were correlated with the MR findings. Overall, the accuracy of MR imaging for determination of patency was 100%. In patients with angiographic correlation and technically adequate MR examinations, MR imaging results were used to identify or exclude stenoses correctly in 66.7% of patent vessels. The four missed or underestimated stenoses occurred in vessels 10 mm or less in diameter.