Nonalcoholic fatty liver disease (NAFLD) consists of a broad spectrum of liver lesions ranging from fatty liver (FL), through nonalcoholic steatohepatitis (NASH), up to cirrhosis. The incidence of nonalcoholic fatty liver disease has increased in recent years due to the high rate of obesity in developed countries. Although the dogma "simple steatosis - benign prognosis, nonalcoholic steatohepatitis - severe evolution" still stands for many hepatologists, plenty of data underline the unsuspected evolution, i.e., that some patients may progress from fatty liver towards cirrhosis and hepatocellular carcinoma (HCC). NAFLD is the hepatic manifestation of the metabolic syndrome. In certain metabolic circumstances, isolated hepatic steatosis is not necessarily a benign disorder associating cardiovascular risk and evolution towards severe liver diseases including HCC. We tried to shed some light on this problem, taking into account its major health impact and the variegate and sometimes unpredictable evolution of NAFLD.