Exposure to risk factors such as diabetes mellitus and hyperlipidemia decrease the bioavailability of endothelium-derived nitric oxide (NO) and impairs endothelium-dependent vasodilation. Circulating concentrations of an endogenous inhibitor of NO synthase, asymmetric dimethyl-L-arginine (ADMA), has been linked to endothelial dysfunction. It appears to be an independent risk factor for future cardiovascular events and total mortality. The purpose of this study is to investigate serum concentrations of ADMA correlate to diabetes mellitus and hyperlipidemia compared with the healthy subjects. A total of 300 subjects were recruited for the present study (100 normal healthy subjects, 52 males and 48 females); (100 diabetic patients, 51 males and 49 females); (100 hyperlipidemic patients, 50 males and 50 females). Serum concentrations of ADMA were measured with the use of ELISA. The concentration of ADMA were significantly higher (p < 0.001) in diabetic and hyperlipidemic patients in both sexes when compared with their matched control subjects. A positive correlation was obtained between ADMA and glucose of diabetic males (r = 0.40, p = 0.01) and females (r = 0.51, p = 0.01). In addition, a positive correlation was also obtained between ADMA and lipid profile of hyperlipidemic males (total cholesterol: r = 0.71, p = 0.01; triacylglycerol: r = 0.70, p = 0.01; low density lipoprotein cholesterol: r = 0.34, p = 0.05) and females (total cholesterol: r = 0.77, p = 0.01; triacylglycerol: r = 0.51, p = 0.01; low density lipoprotein cholesterol: r = 0.46, p = 0.01). The present study reveals that serum ADMA concentrations are elevated in disorders associated with vascular endothelial dysfunction such as diabetes mellitus and hyperlipidemia. However, endothelial dysfunction is considered as early event in the process of atherogenesis.