The left internal thoracic artery (LITA) undergoes vascular remodelling when used for coronary artery bypass grafting. In this study we tested the hypothesis that the extent of the LITA remodelling late after coronary artery bypass grafting assessed by multidetector computed tomography is related to the severity of stenosis in the native coronary vessel. One hundred and forty-two patients who had undergone coronary artery bypass grafting including implantation of LITA as conduit to the left anterior descending artery were studied 5 years after surgery. Arterial graft patency and geometry was assessed with 64-slice multidetector computed tomography. Quantitative volumetric assessment of the LITA was performed to measure the average vessel lumen area (mm2/m2). The native coronary vessel subtended by the LITA was evaluated by multidetector computed tomography and defined as a high-grade stenosis patient group, when the diameter stenosis was>70% and an intermediate grade stenosis patient group when <70%. Among patients with intermediate-grade stenosis of the native vessel 11 out of 65 patients (17%) had a totally occluded LITA, as opposed to none among the 77 patients with a high-grade stenosis. In patients with intermediate-grade stenosis of the proximal native vessel, the LITA lumen area was 4.9 compared to 5.3 mm 2/m2 in patients with a high-grade stenosis of the proximal native vessel (P = 0.0043). Lumen area of the LITA when used as a conduit in patients with coronary artery disease seems to be inversely correlated with the severity of disease in the native coronary vessel proximal to the anastomosis. Volumetric vessel multidetector computed tomography appears to be useful for evaluation of coronary bypass remodelling.