Nonalcoholic fatty liver disease (NAFLD) and childhood obesity are emerging global health issues. The aim of this study was to identify a simple predictor of NAFLD in children and adolescents. This community-based study was conducted from December 2012 to September 2013 in Taiwan and included 1,222 children between 10 and 19 years of age. After excluding alcohol consumption and hepatic-related lesions, NAFLD was diagnosed according to sonographic criteria. Potential confounding factors (including age, gender, and anthropometric and laboratory data) were tested by logistic regression analysis. The cutoff value was determined using receiver operating characteristic (ROC) curve analysis. In addition to older age, heavier weight, and wider waist, subjects with NAFLD had significantly higher blood pressure, lipid disturbances, and alanine aminotransferase/aspartate aminotransferase (ALT/AST) ratios. The correlation between NAFLD and ALT/AST ratio remained significant even after adjusting for confounders (adjusted odds ratio [OR], 2.19; 95% confidence interval [CI], 1.24-3.87; p = .007). The risk score of having a fatty liver, based on ALT/AST ratio, was greater than 0.981 according to ROC curve analysis (sensitivity, 60.5%; specificity, 80.3%; area under the curve, 0.756; CI, 0.71-0.80; p < .001). Therefore, ALT/AST ratio may represent a powerful index of hepatosteatosis in children and adolescents.