The non alcoholic fatty liver disease (NAFLD) manifests with liver damage and it is associated with obesity. The objective of this work was to detect the risk of obese school students of developing NAFLD, through an analytical, observational study, comparing their liver function with that of a control group, and its relationship with physical activity, dietary, biochemical and anthropometric variables. One hundred and sixty school students (ages 7-11) were evaluated according to their socio-economic status; nutritional status by the body mass index (BMI) and mid-upper arm fat area (MUAC) (Project Venezuela 1994); body fat percentage by anthropometry (% BF), waist circumference (WC); and metabolism by oral glucose tolerance, basal insulin and post-load glucose, total cholesterol (TC), cLDL, cVLDL, cHDL, triglycerides (TG), glutamic oxaloacetic transaminase (GOT), glutamic pyruvic transaminase (GPT), gamma glutamil transpeptidasa (GGTP) and albumin. Their diet was analyzed by the 24-hour recall and their physical activity by a clinical trial. Mean levels of GPT (p < 0.05), greater frequencies of elevated GOT and GPT (p < 0.05) and lower albumin levels (p < 0.05) were observed in 88 obese school students when compared to controls. The GPT correlated significantly with the BMI, MUAC, % BF, WC, basal insulin and post-load glucose, HOMA, cVLDL, cHDL and TG, while the GOT correlated with MUAC and the GGTP with MUAC, basal insulin, HOMA and cLDL. Albumin was negatively correlated with BMI, MUAC, % BF and WC. TGP reflected better the hepatic compromise of obesity. To assess the risk of NAFLD, the TGO/TGP values should be standardized according to age, gender and race.