The aim of this study was to evaluate 64-slice spiral multidetector computed tomography (MDCT) angiography in the detection of functionally relevant coronary artery stenosis (CAS) using gated myocardial perfusion SPECT (gated SPECT). Methods: Sixty-five patients (62짹9 years, 36 men) with suspected or known coronary artery disease were investigated using 64-slice MDCT angiography and gated SPECT within 2 months. Patients who had a cardiac intervention within this period and those with history of coronary artery bypass graft, intracoronary stent and motion artifacts were excluded. Stenoses with luminal narrowing of ���50% were defined as "significant" in MDCT angiography, which was compared with gSPECT with respect to the detection of functionally relevant CAS. Results: Among 65 patiets 20 (31%) have 34 (13%) perfusion defects (3 fixed) in gated SPECT. MDCT angiography detected significant CAS in 53 (20%) of 260 coronary arteries and 25 patients (38%) had significant CAS. The sensitivity, specificity, and postitive and negative predictive values of MDCT angiography in detecting any perfusion defects on gated SPECT were 90%, 82%, 69%, and 95%, respectively, in patient-based analysis and 88%, 89%, 54% and 98%, respectively, in vessel-based analysis. The sensitivity, specificity, and postitive and negative predictive values of MDCT angiography in detecting reversible perfusion defects on gated SPECT were 88%, 82%, 65%, and 95%, respectively, in patient-based analysis and 86%, 90%, 53% and 98%, respectively, in vessel-based analysis. Conclusion: Sixty-four slice MDCT angiography showed excellent negative predictive value but relatively low postive predictive value. Thus, it can be used to exclude functionally relevant CAS in symptomatic patients with suspected or known CAD. However, gated SPECT remains mandatory for evaluating the functional relevance of CAS.