Non-alcoholic fatty liver disease is increasingly prevalent in children, together with obesity. Transaminases, tests for insulin resistance, ultrasonography and MRI are variably used as surrogates markers of steatosis. Other liver diseases, such as Wilson disease, should be excluded. A liver biopsy is performed in selected cases: young children, familial history of severe disease, inconclusive tests for other pathologies, suspected advanced fibrosis, hypertransaminasemia despite weight loss and in clinical trials. Weight reduction, and changes in lifestyle, are the front-line treatment. Drug therapy is under evaluation.