To assess the relationship between epicardial coronary artery stenosis severity and the corresponding regional transmural perfusion at rest and during adenosine stress, using multidetector computed tomography (MDCT). We evaluated the relationship between the severity of coronary artery diameter stenosis assessed by MDCT angiography and semi-quantitative myocardial MDCT perfusion in 200 symptomatic patients. The perfusion index (PI = mean myocardial attenuation density/mean left ventricular lumen attenuation density) at rest and during adenosine stress, the myocardial perfusion reserve (MPR = stress − PI/rest − PI), and the transmural perfusion ratio (TPR = subendocardium/subepicardium) were calculated. A coronary artery stenosis ≥50 % was present in 49 patients (25 %). Rest-PI and rest-TPR values were similar in patients with and without a coronary artery stenosis ≥50 %, whereas stress-PI, stress-TPR and MPR were significantly reduced in patients with a stenosis ≥50 % (p