Nonalcoholic steatohepatitis (NASH), one of the NAFLDs (nonalcoholic fatty liver diseases), is regarded as a hepatic manifestation of metabolic syndrome. NASH can progress to cirrhosis, and possibly to hepatic malignancy. Currently, liver biopsy is the only reliable method of assessing the presence or absence of NASH and the stage of fibrosis. The finding of steatosis with evidence of hepatocyte injury such as inflammation, ballooning, degeneration, and/or fibrosis, is generally essential for making a diagnosis of NASH. However, its diagnostic criteria have not yet been established. The pathologic findings of NASH and related diseases, and the grading system currently in use are reviewed herein.