Non-alcoholic fatty liver disease (NAFLD) and non-alcoholic steatohepatitis (NASH) are the hepatic manifestations of the metabolic syndrome. Since the prevalence of obesity and consequently of the metabolic syndrome is steadily increasing, the different types of NAFLD are nowadays the most common cause of liver injury in North America. The development of NASH and fatty liver cirrhosis occurs after a "two-hit-theory", in which hepatic steatosis is followed by lipid peroxidation, the production of cytokines and the induction of Fas ligand. A standardized drug based therapy does not exist so far, but glitazones have emerged as a promising treatment option. However, since the disease is related to Western lifestyle, treatment should be based on prevention and changes in lifestyle.