Background/aims: The incidence of non-alcoholic fatty liver disease has been increasing parallel to obesity in the pediatric age group. This study aimed to analyze the factors that are related to non-alcoholic fatty liver disease in obese children. Methods: 101 obese children and 68 non-obese controls were included in the study. Liver steatosis was investigated by ultrasonography. The subjects were divided into three groups: 53 obese patients with fatty liver (Group 1), 48 obese patients without steatosis (Group II), and 68 controls without steatosis (Group III). Group I was further divided into those with Grade 1 steatosis (44 patients, Group Ia) and higher grades of steatosis (9 patients, Group Ib). The relationships of body mass index, serum ALT, lipids, leptin, and insulin resistance index with steatosis were analyzed. Results: 52.4% of obese children had fatty liver and 13.8% had high ALT levels. Additionally, all patients with elevated ALT levels were seen to have liver steatosis by ultrasonography. Leptin and insulin resistance index levels were higher in obese groups than controls; however, the difference disappeared when these levels were adjusted for body mass index. ALT levels were higher in Group I (31.5 +/- 30.2) than Group II (18.0 +/- 7.1) and Group III (14.5 +/- 5.2) (p<0.05). Group Ib showed higher VLDL and ALT levels than Group la (p<0.05). Multiple regression analysis revealed that body mass index was the most important determinant of liver steatosis, while body mass index and VLDL were the determinants of higher ALT levels. Conclusions: We suggest that body mass index and VLDL are the most important determinants of non-alcoholic fatty liver disease and elevated ALT levels in obese children. The contribution of leptin to this process could not be determined in our findings.