It is estimated that 30%of the adult population in Japan is affected by nonalcoholic fatty liver disease(NAFLD).Fatty changes of the liver are generally diagnosed using imaging methods such as abdominal ultrasonography(US)and computed tomography(CT),but the sensitivity of these imaging techniques is low in cases of mild steatosis.Alanine aminotransferase levels may be normal in some of these patients,warranting the necessity to establish a set of parameters useful for detecting NAFLD,and the more severe form of the disease,nonalcoholic steatohepatitis(NASH).Although liver biopsy is currently the gold standard for diagnosing progressive NASH,it has many drawbacks,such as sampling error,cost,and risk of complications.Furthermore,it is not realistic to perform liver biopsies on all NAFLD patients.Diagnosis of NASH using various biomarkers,scoring systems and imaging methods,such as elastography,has recently been attempted.The NAFIC score,calculated from the levels of ferritin,fasting insulin,and typeⅣcollagen 7S,is useful for the diagnosis of NASH,while the NAFLD fibrosis score and the FIB-4 index are useful for excluding NASH in cases of advanced fibrosis.This article reviews the limitations and merits of liver biopsy and noninvasive diagnostic tests in the diagnosis of NAFLD/NASH. It is estimated that 30% of the adult population in Japan is affected by nonalcoholic fatty liver disease (NAFLD) .Fatty changes of the liver are generally diagnosed using imaging methods such as abdominal ultrasonography (US) and computed tomography (CT), but the sensitivity of these imaging techniques is low in cases useful for detecting NAFLD, and the more severe form of the disease, nonalcoholic steatohepatitis (NASH) .Although liver biopsy is currently the gold standard for diagnosing progressive NASH, it has many drawbacks, such as sampling error, cost, and risk of complications. It’s not realistic to perform liver biopsies on all NAFLD patients. Diagnosis of NASH using various biomarkers, scoring systems and imaging methods, such as elastography, has recently been attempted. NAFIC score, calculated from the levels of ferritin, fasting insu lin, and typeⅣcollagen 7S, is useful for the diagnosis of NASH, while the NAFLD fibrosis score and the FIB-4 index are useful for excluding NASH in cases of advanced fibrosis. This article reviews the limitations and merits of liver biopsy and noninvasive diagnostic tests in the diagnosis of NAFLD / NASH.