AIM:　To　determine　the　diagnostic　performance　of　instantaneous　wave-free　ratio　(iFR)　derived　from　non-invasive　coronary　computed　tomography　angiography　(CTA;　iFR(CT))　for　ischaemia-causing　coronary　stenosis,　and　to　compare　the　diagnostic　efficacy　of　iFR(CT),　CTA,　and　CTA　plus　iFR(CT).　METHODS　AND　MATERIALS:　Thirty-nine　patients　(55　vessels)　with　known　or　suspected　coronary　artery　disease　were　included.　All　patients　underwent　invasive　coronary　angiography　and　fractional　flow　reserve　(FFR)　according　to　CTA　findings　and　clinical　indicators.　The　same　raw　data　used　for　CTA　were　used　to　build　patient-specific　computed　flow　dynamic　models　and　to　calculate　iFR(CT).　RESULTS:　On　a　vessel-based　level,　the　correlation　between　iFR(CT)　and　FFR　was　moderate　(r=0.65,　p＜0.05);　the　optimal　iFR(CT　)cut-off　value　was　0.85　based　on　an　FFR　cut-off　value　of　0.80,　resulting　in　85%　sensitivity,　69%　specificity,　61%　positive　predictive　value　(PPV),　89%　negative　predictive　value　(NPV),　and　75%　accuracy.　The　AUC　showed　significant　differences　between　iFR(CT)　and　CTA　(vessel-based:　0.84　versus　0.68;　patient-based:　0.84　versus　0.62;　both　p＜0.01).　The　accuracy　of　CTA　combined　with　iFR(CT)　was　significantly　increased　compared　to　CTA　alone　for　vessels　with　intermediate　stenosis　(83%　versus　40%,　p＜0.01).　CONCLUSION:　iFR(CT)　showed　better　diagnostic　performance　than　CTA.　iFR(CT)　may　be　a　promising　method　for　detection　of　ischaemia-causing　coronary　stenosis,　even　in　vessels　with　intermediate　stenosis.　(C)　2018　The　Royal　College　of　Radiologists.　Published　by　Elsevier　Ltd.　All　rights　reserved.