Background: Absence of coronary artery calcium (CAC) in asymptomatic patients is associated with a very low risk of future cardiovascular events. However diagnostic significance of calcium score zero in symptomatic patients is not clearly defined. With emergence of 64-slice multidetector CT (MDCT), coronary artery calcium scoring and coronary artery Stenosis can be evaluated simultaneously. We sought to determine the significance of calcium zero in diagnosing significant Stenosis with 64-MDCT. Methods: We enrolled a total of 1028 consecutive patients who had symptoms of coronary artery disease and underwent coronary calcium scan and coronary CT angiography. Nondiagnostic image quality and congenital anomaly of coronary artery were excluded. Finally, we included a total of 986 patients in the analysis. Significant Stenosis of coronary artery was defined more than 50% diameter narrowing. The significance of absence of coronary calcium was analyzed in men and women. Results: Men were 515 (mean age짹SD=57.9짹11.8). Women were 471 (mean age짹SD=60.7짹9.8). CAC was absent in 231 (44.9%) men and in 270 (57.3%) women. In men, significant Stenosis was in 118 patients (22.9%). CAC was absent in 9 of them; 7 one vessel disease and 2 left main disease. Four patients underwent invasive coronary angiography and stenting was done in 3 and bypass surgery in 1. Sensitivity, specificity, positive and negative predictive values of presence of calcium in diagnosis of significant stenosis were 92%, 56%, 38%, 96%, respectively. In women, significant Stenosis was in 56 patients (11.9%). CAC was absent in 1 of them which was one vessel disease. After confirming significant stenosis by using invasive coronary angiography, the patient was treated by stenting. Sensitivity, specificity, positive and negative predictive values in women was 98%, 65%, 27%, 100%, respectively. Conclusion: In women, significant stenosis can be excluded by absence of CAC with high negative predictive value. However, in men, even in the absence of CAC approximately 4% had a significant stenosis, which were mostly one vessel disease.