Plasma asymmetric dimethylarginine (ADMA) is a novel risk factor for atherosclerosis and has been observed to associate with endothelial function in cross-section studies. In the present study our aim was to investigate whether plasma ADMA levels are predictive of brachial artery endothelial function in a prospective setting.Using ultrasound we measured brachial artery flow-mediated dilation (FMD) both in 2001 and 2007 in 1808 healthy subjects aged 24–39 years at baseline. Plasma methylarginines were determined by isocratic high-pressure liquid chromatography in 2001. In a multivariable model adjusted with brachial diameter and conventional cardiovascular risk factors, baseline ADMA levels had a significant inverse association with FMD measured 6 years later (β±SE: −1.89±0.69%, P=0.006).We conclude that plasma ADMA can predict brachial artery FMD in subjects without prevalent atherosclerotic disease. These data suggest that plasma ADMA may have a determinative role in predicting endothelial function.