Asymmetric dimethylarginine (ADMA) is an amino acid that looks like arginine and exists in plasma, urine and tissues. ADMA occurs naturally by methylation of arginine remnants in proteins and the studies about it increases every day. ADMA, as a major inhibitor of nitric oxide sentase is accepted as cardiovascular risk factor. In this review, the knowledge about metabolism, the relation of ADMA with several patologies, primarily endothelial dysfunction and the measurement methods were overviewed and the results of clinical and experimental studies were discussed.