Non-alcoholic fatty liver disease is a clinicopathological condition that comprises a wide spectrum of liver damage, ranging from simple steatosis to steatohepatitis, advanced fibrosis and cirrhosis. Non-alcoholic steatohepatitis represents only a stage within the spectrum of non-alcoholic fatty liver disease and is defined pathologically by the presence of steatosis together with necro-inflammatory activity. The true prevalence of non-alcoholic fatty liver disease is unknown, but it is estimated that it affects 10-24% of the general population in different countries. The diagnosis of non-alcoholic fatty liver disease is based upon convincing evidence of absent or minimal alcohol consumption, compatible histological changes in liver biopsy and the exclusion of other liver diseases. The natural history of non-alcoholic fatty liver disease remains to be defined. Patients with pure steatosis on liver biopsy follow a relatively benign course, whereas patients with histological necro-inflammatory changes and/or fibrosis may progress to end-stage liver disease. An initial step in the treatment of non-alcoholic fatty liver disease is the management of associated conditions, such as obesity, diabetes mellitus and hyperlipidaemia. Non-alcoholic fatty liver disease patients with steatohepatitis and/or fibrosis on liver biopsy may benefit from investigational pharmacological therapy. Patients with decompensated cirrhosis from non-alcoholic fatty liver disease may be candidates for liver transplantation.