Non-alcoholic fatty liver disease (NAFLD) represents one of the most common forms of liver disease and is considered the hepatic manifestation of the metabolic syndrome. Within the NAFLD spectrum, simple steatosis is considered benign, whereas non-alcoholic steatohepatitis (NASH) may progress to cirrhosis. The distinction can be made only by liver biopsy. There is not complete agreement on criteria for diagnosis or the features used for grading and staging lesions. This article reviews some of the studies dealing with the histopathology of NAFLD, with attempts to develop a standardized pathologic scoring system for NASH.