Recently, obesity (BMI>or=25 kg/m2) and type II diabetes mellitus have reached epidemic proportions in Korea, and rates of nonalcoholic fatty liver disease (NAFLD) are between 10% and 25% of the general population. NAFLD in Korea is as closely associated with several components of metabolic syndrome including, obesity, hypertension, diabetes and dyslipidemia as it is in Western countries. Insulin resistance and hyperinsulinemia may play a role in the pathogenesis of fatty liver in patients with normal body weight as well as in patients with obesity. And, obesity induced accumulation of fat in the adipose tissue leads to an imbalance in the regulation of adipokines, such as downregulation of adiponectin and upregulation of retinol-binding protein 4 (RBP4) and ghrelin. High BMI, the AST/ALT ratio, and ALT levels could be used to distinguish NASH from simple steatosis in Korean patients. In large number of NAFLD patients who underwent a voluntary medical checkup, even a small weight reduction was associated with improvements in their hepatic steatosis grade on ultrasonography, serum aminotransferase levels, and related metabolic abnormalities. Subjects with fatty liver disease should be advised to lose weight through lifestyle modifications. Small animal and human studies of treatment with PPAR agonists and betaine have been reported in the Korean literature. It is now acknowledged that NAFLD is the most common liver disease in Korea, largely due to the considerable increase in metabolic abnormalities such as obesity and diabetes. Future studies should continue to focus both on the pathogenesis and the treatment of NAFLD in order to accumulate more of our own data.