Although impaired synthesis and/or bioavailability of nitric oxide are considered to contribute to insulin resistance and the progression of liver disease in nonalcoholic fatty liver disease, role of asymmetric dimethylarginine, an endogenous inhibitor of nitric oxide synthase, has not been examined. We examined retrospectively which anthropometric and metabolic parameters were independently associated with serum levels of asymmetric dimethylarginine in nonalcoholic fatty liver disease. A total of 194 consecutive biopsy-proven nonalcoholic fatty liver disease patients with or without type 2 diabetes were enrolled. Serum asymmetric dimethylarginine levels in nonalcoholic fatty liver disease patients were significantly higher, irrespective of the presence or absence of diabetes, than those in healthy control. Multiple stepwise regression analysis showed that decreased total protein and procollagen N-terminal peptide levels, markers of advanced liver disease and hepatic fibrosis, respectively, were independently associated with asymmetric dimethylarginine levels in nonalcoholic fatty liver disease subjects without diabetes, whereas soluble form of receptor for advanced glycation end products and density ratio of liver to spleen in computed tomography were independent correlates of asymmetric dimethylarginine in diabetic patients. The present study suggests that asymmetric dimethylarginine may be associated with nonalcoholic fatty liver disease, especially subjects without diabetes.