Fatty liver disease (FLD) is the term used to describe a spectrum of liver disorders characterized by macrovesicular steatosis. In adults and adolescents alcohol consumption in amounts considered to be harmful to the liver must be excluded. Because of the likehood of having FLD is directly proportional to body mass index, given the increasing prevalence of obesity, nonalcoholic FLD (NAFLD) is an important public health problem. There are two recognized histologic pattern of NAFLD: fatty liver alone and steatohepatitis (NASH). The latter represents a shift from simple steatosis to an inflammatory component. NASH is described by grading that indicates the activity of the inflammatory lesion and by staging that reflects the progressive degree of fibrosis. The presence of fat in the liver can be suggested by various imaging modalities, however no current non invasive methods can distinguish NASH from NAFLD. Liver biopsy remains the gold standard for staging and grading. The presence, degree and pattern of aminotransferase elevation are non specific and do not distinguish between fatty liver alone and NASH. Prevalence of FLD in unselected children is about 10% and it increases with age; in selected population such as obese children it reaches about 50% al cases. Obesity and insulin resistance are key factors in exacerbating hepatic inflammation and fibrogenesis. There is no effective treatment of NAFLD, but there are several approach to this problem including weight reduction by diet and exercise, pharmacologic treatment of insulin resistance and use of drugs such as antioxidant (α-tocopherol) or insulin sensitizer such as metformin