Non alcoholic fatty liver disease (NAFLD) is a recently recognized entity related to modern lifestyle and with expanded clinical importance because of the rising incidence of obesity and diabetes. NAFLD is considered as the hepatic complication of the metabolic syndrome as its hallmark is insulin resistance, with no definite treatment to date. It corresponds to a spectrum of lesions ranging from isolated steatosis (non alcoholic fatty liver or NAFL) to cirrhosis. Until now, liver biopsy is the only tool to assess the presence of non alcoholic steatohepatitis (NASH), the progressive form of the disease. The NAFLD/NASH pathogenesis involves several potential mechanisms into a multi step process.