Clinical and pathological features were reviewed in 76 Japanese patients with non-alcoholic steatohepatitis (NASH). Forty-one were male and 35 were female with the mean age of 49.7 years old (range 15-75 years old, males; 46.3, females; 53.7 years old). Fifty-four percent of patients were preobese with a body mass index (BMI) between 25 and 30, while 16% of the patients were non-obese, and only 30% of the cases were morbidly obese, indicating that Japanese have a greater tendency to develop insulin-resistance and fatty liver disease than Western people. Hyperlipidemia was found in 51%, diabetes mellitus in 38%, and hypertension in 33% of the patients. Abnormally elevated liver function tests were found in one-third to two-thirds of the patients and were characteristically mild with 2- to 3-fold elevation from the normal range in the majority of the cases. Histological features of the liver were similar or identical to those reported in English literature and were characterized by fatty change, perivenular and pericellular fibrosis in zone 3, hepatocyte ballooning and necrosis with occasional Mallory's body formation and polymorphonuclear leukocyte infiltration. Mallory's bodies were found in 39% of patients and were characteristically small and poorly formed compared with those in alcoholic hepatitis. Eosinophilic granular or dirty foggy aggregated, not sufficient to be identified as Mallory's bodies, were a rather characteristic cytoplasmic expression in NASH patients. Portal inflammation and fibrosis were not found in the early stage of NASH, but were found as the disease progresses with formation of C-C and/or P-C bridging fibrosis, and eventually resulting in liver cirrhosis.