PURPOSE Primary prevention of atherosclerotic cardiovascular disease has become an issue of major public health interest, according to increasing awareness of the substantial risks posed by asymptomatic atherosclerosis. With the advent of multi-slice CT technology, coronary CT angiography (CTA) allows for direct visualization of the coronary arteries in a noninvasive manner. It was the aim of this study to evaluate the prevalence of occult CAD with CCTA and to evaluate the potential of this advanced technology to impact risk stratification in middle-aged asymptomatic individuals. METHODS We consecutively enrolled 3368 asymptomatic middle-aged (35~75 years) South Korean individuals (2011 men and 1357 women; aged 50짹9 years). Subjects were free of known cardiovascular diseases and symptoms and had undergone CTA evaluation using 64-slice MDCT for general routine health evaluation from October 2006 until February 2008. RESULTS Atherosclerotic plaque were present in 822 of 3368 (25%) individuals. 108 subjects had significant (>50%) diameter stenosis on CTA and 24 had severe (>75%) stenosis. The prevalence of significant stenosis in low-, moderate-, moderately high-, high-NECP risk subjects were 1, 3.7, 8.2 and 8.5%, respectively. On multivariate analysis, independent predictors of atherosclerotic plaque were age, male gender, diabetes, hypertension, LDL (>130mg/dl) (p<0.001), whereas those of significant stenosis were age, male gender, diabetes, hypertension, LDL and smoking (p<0.001). CONCLUSION The present study demonstrated that the prevalence of occult CAD in apparently healthy individuals was not negligible. Although further studies including outcomes and cost-effectiveness need to be, CTA provides opportunity to detect occult CAD in asymptomatic individuals in a non-invasive manner and may provide a better insight about the occult CAD.