In the absence of alcohol consumption, non-alcoholic fatty liver disease (NAFLD) refers to a range of lesions from steatosis (non-alcoholic fatty liver, or NAFL) to a complicated pattern including hepatocellular injury and inflammation (non-alcoholic steatohepatitis, or NASH). It is becoming more evident, though, that there might be some intermediary patterns. Since a specific definition of each group is crucial, the histological assessment of liver biopsy samples is essential in the diagnosis of NAFLD and NASH in the absence of adequate noninvasive procedures. In a suitable clinical setting, patients can be classified as having NAFLD if at least 5% of their hepatocytes show steatosis. The lesion is typically classified as NASH when lobular inflammation and liver cell clarification/ballooning are also present. Since fibrosis stage is the primary predictor of prognosis for this condition, evaluating it is even more important than necroinflammation. Although semi-quantitative histological grading methods for NAFLD have been proposed, they are not practical in clinical practise and each has certain drawbacks. For thoroughness, we advise using the SAF (Steatosis, Activity, Fibrosis) score, which evaluates each of the three histopathological lesions in NAFLD separately based on the degree of steatosis (S, from S0 to S3), degree of activity (A, from A0 to A4 by adding grades of ballooning and lobular inflammation, both from 0 to 2), and stage of fibrosis (F from F0 to F4).