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Non-alcoholic fatty liver disease (NAFLD) represents a spectrum of disease ranging from hepatocellular steatosis through steatohepatitis to fibrosis and irreversible cirrhosis. The prevalence of NAFLD has risen rapidly in parallel with the dramatic rise in obesity and diabetes,1,2 and is rapidly becoming the most common cause of liver disease in Western countries.3 Indeed, NAFLD is now recognized to be the aetiology in many cases previously labelled as cryptogenic cirrhosis.4 In Western populations, estimates of NAFLD prevalence vary between 20 and 30%,5,6 rising up to 90% in morbidly obese individuals.7 The more severe, and clinically significant form of NAFLD, non-alcoholic steatohepatitis (NASH) is less common, affecting an estimated 2–3% of the general population,8 and up to 37% of the morbidly obese.7 Of particular concern, and with significant implications for future disease burden, is the increasing prevalence of NAFLD in children and young adults. Studies have reported a 3% prevalence of NAFLD in the general paediatric population, rising to 53% in obese children.9,10 NAFLD has a strong association with type 2 diabetes, with steatosis present in 70% of type 2 diabetics screened with ultrasound,11 and thus it is now recognized to represent the hepatic manifestation of the metabolic syndrome. NAFLD occurs in all ethnic groups although it appears to have a lower prevalence in African-Americans compared with Hispanic and European Americans. This difference remains even after controlling for obesity and insulin resistance (IR)5,12 and may be related to ethnic differences in lipid homeostasis.5 There are no laboratory, imaging or histological findings which can accurately distinguish between NAFLD and alcohol-induced steatosis or steatohepatitis, and the diagnosis can therefore only be made in the absence of a history of significant alcohol intake. Other specific causes … Address correspondence to J. K. Dowman, Centre for Liver Research, Institute of Biomedical Research, University of Birmingham, Wolfson Drive, B15 2TT, Birmingham, UK. email: j.k.dowman{at}bham.ac.uk