Non-alcoholic fatty liver disease (NAFLD) regroups all liver disease stages characterized by an increased amount of fat within the liver, and is associated in the majority of the patients with the presence of a metabolic syndrome. The prevalence of NAFLD is increasing, together with the inflammatory condition called non-alcoholic steatohepatitis (NASH) characterized not only by steatosis but also by lobular inflammation and hepatocyte injury. NASH is associated with an increased liver-related (for advanced fibrosis stages) and non-liver-related morbidity and mortality (mainly due to cardiovascular events). While NASH is a histologically proven diagnosis, both steatosis and fibrosis could be evaluated by non-invasive methods allowing adequate treatment and follow up.