Background: The absence of coronary artery calcium (CAC) is a marker of very low cardiovascular risk. Endothelial cells may have an effect on the initiation and propagation of arterial calcification. We aimed to identify the relationship between the absence of CAC and endothelial function in individuals without cardiovascular disease and diabetes. Methods and Results: CAC was assessed using electron-beam computed tomography and the calcium score was then computed. Endothelial function was measured by assessing reactive hyperemia-induced vasodilation and expressed by the reactive hyperemia index (RHI). Of 82 patients, 39 had non-detectable calcium (CAC score=0) and 43 had a CAC score >0. In the CAC score. group, the prevalence of normal endothelial function was 84.6%, compared to 48.8% in the CAC score >0 group, P=0.001. The absence of CAC was highly correlated with normal endothelial function (gamma=0.704, P<0.001). On average, endothelial function was significantly better in the CAC score=0 group than in the CAC score >0 group (RHI 2.2 +/- 0.6 vs. 1.8 +/- 0.5, P=0.002). In a multivariate logistic regression model, only normal endothelial function (odds ratio [OR] 5.03, 95% confidence interval [CI] 1.55-16.27, P=0.007) and age (years) (OR 0.91, 95% CI 0.86-0.96, P=0.002) were independently associated with the absence of CAC. Conclusions: Normal functional status of the vasculature may be important for the prevention of coronary calcification and may partly account for the low cardiovascular risk of absent CAC. (Circ J 2012; 76: 2705-2710)