OBJECTIVE: To investigate the prevalence of non-alcoholic fatty liver disease (NAFLD) as well as the determination of associated metabolic abnormalities in Iranian school-aged children and adolescents. METHOD: Data were obtained from 966 children aged 7-18 years in Iran by a cross-sectional survey in 2007. These children were subjected to a complete anthropometric and laboratory measurement and abdominal ultrasonography for liver echogenicity and size. A questionnaire was also used to obtain information on demographical and medical history, dietary habit, alcohol consumption and cigarette smoking. RESULTS: Fatty liver was diagnosed by ultrasound in 7.1% of children. The prevalence of elevated alanine aminotransferase (ALT) was 1.8%. NAFLD was significantly more common in the older group (12.5 against 3.5%, P<0.0001). The odds ratios (OR) (95% confidence interval) for NAFLD in children having elevated ALT, high fasting insulin, total cholesterol, low density lipoprotein (LDL) cholesterol, triglyceride and insulin resistance (IR) were 10.9 (3.9-30.4), 2.8 (1.6-4.8), 2.8 (1.5-5.1), 2.8 (1.5-5.3), 2.5 (1.3-4.8) and 4.4 (1.6-12.3) respectively. Therefore, NAFLD was significantly associated with increasing age, ALT, fasting insulin, total cholesterol, LDL cholesterol, triglyceride and IR. In multiple logistic regression analysis, ALT (OR=1.2; P<0.01), total cholesterol (OR=1.01; P<0.01) and waist circumference (OR=1.14, P<0.0001) were independent metabolic factors predictive of NAFLD after adjustment for other variables. CONCLUSION: There was a strong relationship between NAFLD and the abnormal metabolic variables in children. It will be very useful if children are assessed for variables such as waist circumference, fasting blood sugar, fasting insulin and serum lipid profile in order to screen those susceptible to NAFLD.