AIM: To investigate the potential association of circulating zonulin with the stage of liver disease in obese children with biopsy-confirmed nonalcoholic fatty liver disease (NAFLD). METHODS: A case-control study was performed. Cases were 40 obese children with NAFLD. The diagnosis of NAFLD was based on magnetic resonance imaging (MRI) with high hepatic fat fraction (HFF >= 5%), and confirmed by liver biopsy with >= 5% of hepatocytes containing macrovesicular fat. Controls were selected from obese children with normal levels of aminotransferases, and without MRI evidence of fatty liver as well as of other causes of chronic liver diseases. Controls were matched (1-to 1) with the cases on age, gender, pubertal stage and as closely as possible on body mass index-standard deviation score. All participants underwent clinical examination, laboratory tests including zonulin, inflammatory and metabolic parameters, and MRI for measurement of HFF and visceral adipose tissue. RESULTS: Zonulin values were significantly greater in obese subjects with NAFLD than in those without NAFLD [median (interquartile range), 4.23 (3.18-5.89) vs 3.31 (2.05-4.63), P