In the last 15 years evidence has been accumulating suggesting that hepatic steatosis may be the starting point for a progressive liver disease. Nonalcoholic steatosis (nonalcoholic fatty liver disease, NAFLD) is now considered a metabolic pathway to advanced liver disease, cirrhosis and hepatocellular carcinoma. Liver disease of other etiology, namely hepatitis C virus, may interact with NAFLD, although the underlying mechanism(s) have not been fully elucidated. Type 2 diabetes mellitus, obesity and dyslipidemia are the principal factors associated with NAFLD, which is now considered the hepatic expression of metabolic syndrome (MS). Several studies have dealt with the relationship of NAFLD and MS, the risk of liver disease associated with the classical features of MS, the importance of insulin resistance as the common soil of different diseases. We still need to clarify the mechanism(s) responsible for liver disease progression from pure fatty liver, to steatohepatitis and to cirrhosis, and the reason(s) why only a few NAFLD cases progress to terminal liver failure while others (the majority) will have a cardiovascular outcome. The epidemics of obesity and diabetes of Western countries is expected to produce a significant increase of metabolic liver disease in the next years. Prevention and intervention programs based on lifestyle are therefore mandatory to reduce the burden of metabolic liver disease.