Coronary artery calcium scoring (CACS) is a reasonable test for patients with the possibility of atherosclerosis. It can also be used for reclassifying the coronary artery disease (CAD) to the high-risk status by higher CACS and subsequently modifying the management of the patients.The purpose of this study was to investigate the association of CACS to the severity of coronary artery disease in the patients who were scheduled to perform coronary artery angiography (CAG) by tradition. CACS could be a simple, relatively cost-benefit, and noninvasive method for early screening of patients with obstructive coronary artery disease. METHODS In the present study, CAC scoring was evaluated by non-enhanced Multi-Detector Computed Tomography (MDCT) in a total 239 patient suffering from coronary artery disease. Of them, 223 patients were planned to undergo CAG based on clinical examination or other noninvasive diagnostic methods (such as MPI, ETT, EKG or Echo). RESULTS Our results showed that 11 of 67 patients with a negative CACS (zero) had obstructive coronary artery disease derived from the results of CAG. We also found a significant correlation between high CACS (more than 400) and extensive obstructive CAD, except for the two patients who had only mild CAD. There was a linear correlation between CACS and the severity of CAD on the basis of Gensini score and the number of involved arteries (CC=0.507, PV<0.001). Despite fairly high sensitivity (86.6) of zero CAC among patients with a negative score (86%), zero CACS cannot rule out the existence of obstructive coronary artery disease. As we found, increased level of CACS (>400) might be a significant indicative of CAD in referring patients.