We aimed to examine the relationship between epicardial fat thickness (EFT) measured by echocardiography and cardiovascular functional parameters in children with type 1 diabetes mellitus (T1DM). The study included 50 type 1 diabetic children and 50 healthy subjects matched by sex, age, and body mass index. In addition to laboratory tests, all participants underwent transthoracic echocardiography for EFT, cardiac dimensions and left ventricular functions, and ultrasonographic examination for brachial artery fow-mediated dilation (FMD) response and carotid intima-media thickness (CIMT). Multivariate linear regression was used to analyze the relationship between EFT and CIMT, FMD, lateral mitral E' velocity, and mitral E/E' ratio. EFT was signifcantly increased in diabetic children compared with controls (P<0.001). In comparison with controls diabetic children had signifcantly increased mitral A, decreased lateral mitral E', decreased mitral E/A ratio, decreased lateral mitral E'/A' ratio, and increased mitral E/E' ratio (P<0.001). FMD response was signifcantly lower in diabetic group versus controls (P<0.001) and CIMT was signifcantly increased in diabetics versus controls (P=0.03). EFT was negatively correlated with lateral mitral E' velocity (r= −0.613, P<0.001), positively correlated with mitral E/E' ratio (r=0.60, P<0.001), positively correlated with CIMT (r=0.881, P<0.001), and negatively correlated with FMD (r= −0.533, P<0.001). By multivariate regression analysis, the EFT was independently and positively associated with CIMT mean and E/E' mean and negatively associated with FMD mean and E' mean. The cut-of point for EFT as predictor of endothelial dysfunction was 6.95 mm. Our fndings suggest that children with T1DM have subclinical LV diastolic and vascular endothelial dysfunctions associated with increased EFT.