Non-alcoholic fatty liver disease (NAFLD) is one of the most common hepatic disorders in the Western world. Non-alcoholic steatohepatitis (NASH) may occur in a subset of NAFLD patients and is an increasingly recognised clinicopathologial hepatic disorder. NASH may have significant impact on the healthcare system as it is associated with the metabolic syndrome comprising insulin resistance, obesity, hypertension, and type 2 diabetes mellitus. NASH can progress to liver fibrosis, cirrhosis and chronic hepatic failure and eventually to the need for a liver transplantation. The present review deals with the epidemiological features of NASH, describes a two-step pathogenesis with hepatic lipid accumulation (NAFLD) followed by the development of steatohepatitis (NASH). A strategy for establishing a diagnosis of NASH is presented including the indication for liver biopsy. The treatment of NASH may comprise different modalities from diet, weight loss, and exercise to pharmacological treatment to improve insulin resistance and drugs with antioxidant effects.