A high prevalence of childhood obesity has been observed in the last years. Ultrasound of adi-pose tissue is technique validated in adults in order to detect risk of comorbidity as NAFLD and NASH, but no studies at pediatric population. The main objective is to assess measurement of preperitoneal fat by nutritional ultrasound as a screening method for non-alcoholic fatty liver disease (NAFLD) in obese children. Patients and methods: Prospective longitudinal study. A study of somatometry, bioelectrical impedancemetry and nutritional ultrasound has been car-ried out. Results : 102 patients were included, with a mean BMI (SDS) of 2.58. A linear and direct correlation was observed between the fat mass measured by bioelectrical impedancemetry and the total subcutaneous abdominal fat measured by nutritional ultrasound. We also observed a correlation between preperitoneal fat measured by nutritional ultrasound and NASH, with a cut-off point of 0.93 cm of preperitoneal fat (sensitivity 96% and specificity 94%).Conclusions: Measurement of preperitoneal fat by nutritional ultrasound is a good screening method for NASH in obese children.