Clinical and pathological features of 50 Japanese patients with biopsy proven non-alcoholic steatohepatitis (NASH) were reviewed. Incidence of NASH patients increased gradually after 2004, up to 8.06% in the series of liver biopsy specimens. Twenty-six were male and twenty-four were female with a mean age of 54.66 years (range 19-80 years old, male: 47.5, female: 62.4 years old). Forty-four percent of patients were preobese with a body mass index (BMI) between 25 and 30, while 28% of the patients were non-obese, and only 28% of the cases were morbidly obese, confirming that Japanese have a greater tendency to develop fatty liver disease than Western people. Dyslipidemia was found in 30%, diabetes mellitus in 34%, and hypertension in 26% of the patients. Abnormally elevated liver function tests were found in up to 90% of the patients and were characteristically mild with 2- to 3- fold elevation from the normal range in the majority of cases. Histological features of the liver were similar to those reported in Western literature; steatosis was found in every patient and most of them were score 1 (34%) and preferential macrovesicular in type. Lobular necroinflammation was typically mild (combined stage 1 and stage 2, 98%). Ballooned hepatocytes were frequently observed with characteristic small poorly formed Mallory bodies. Pericellular fibrosis, one of the key histologic features of NASH, was classified in stage 1 in the majority of the patients (54%), with characteristic acinar zone 3 involvement. As for the disease progression, portal fibrosis and/or bridging fibrosis could develop leading to liver cirrhosis (stage 4 NASH) in 10% of the patients.