We provide an update review on the prevalence, gender, ethnic variations, and prognosis of nonalcoholic steatohepatitis (NASH). According to annual health checks, 9-30% of Japanese adults have nonalcoholic fatty liver disease (NAFLD) by ultrasonography (US) and prevalence of NASH is estimated to be 1-3%. These conditions are strongly associated with the presence of obesity and lifestyle-related diseases. NAFLD and NASH exhibit age and gender differences in both prevalence and severity. Among younger patients, these conditions are more common in men (2-3 times); however, after 60 years of age, the prevalence of NASH is higher in women. According to a systemic analysis of histological findings for NASH, 37.6% of patients had progressive fibrosis, 20.8% improved, and 41.6% remained stable over a mean duration of follow-up of 5.3 years. Age and presence of inflammation on initial biopsy were independent predictors of progression to advanced fibrosis. The frequencies of development of cirrhosis in NASH are 5-25% during around 7-year follow-up periods. Survival in NASH is lower than the expected survival of the matched general population due to the higher prevalence of cardiovascular and liver-related death. In patients with cirrhotic NASH, hepatocellular carcinoma (HCC) and liver failure are the main causes of morbidity and mortality (5-year cumulative HCC development rate 11.3%, 5-year survival rate 75.2%, respectively). The cumulative rate of recurrence of HCC at 5 years was 72.5%. Regular screening for complications of liver cirrhosis and HCC is extremely important for cirrhotic NASH patients.