The pathophysiology of periodic leg movements (PLMs) in sleep remains to be elucidated. Among other hypotheses an alteration of dopaminergic function has been suggested. Nocturnal urinary dopamine and 4-hydroxy-3-methoxyphenylacetic acid excretion in otherwise healthy subjects with PLMs was significantly reduced (P < 0.001 and P < 0.05, respectively) compared to subjects without PLMs. This finding, for the first time, demonstrates a correlate of a functionally relevant hypoactivity of the dopaminergic system in subjects with PLMs.