Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of nitric oxide (NO) associated with an increased risk of cardiovascular disease (CVD). In this study we assessed the relationship between ADMA and asymptomatic carotid intima-media thickness (CIMT). Eighty subjects underwent a complete history and physical examination, determination of serum chemistries and ADMA levels, and carotid ultrasound investigation (CUI). None of the subjects had symptoms of carotid atherosclerosis and nor were they taking any medication. Statistical analyses showed that high plasma levels of ADMA were positively correlated to CIMT (p less than 0.001). Total cholesterol, low density lipoprotein cholesterol, triglycerides and C-reactive protein plasma concentrations were significantly associated with asymptomatic carotid atherosclerosis (p less than 0.001). High serum concentrations of ADMA were associated with early carotid atherosclerotic lesions as measured by CIMT and represent a new marker of asymptomatic carotid atherosclerosis.