Nonalcoholic fatty liver disease(NAFLD) is recognized as a cause of potentially progressive liver damage. NAFLD is often associated with metabolic syndrome that comprises central obesity, insulin resistance, and hyperlipidemia. Among these, severer forms with histopathological features of increasing ballooned hepatocytes and fibrosis are defined as nonalcoholic steatohepatitis (NASH). The natural history of NASH is only partly known, the disease is slowly progressive and therapeutic outcomes are difficult to define. Since central obesity and insulin resistance are most likely involved in the pathogenesis, justification of life style including physical exercise and nutritional counseling is essential for the treatment of NASH.