Restless legs syndrome (RLS) is a sensorimotor movement and sleep disorder with a high prevalence. While the sleep disturbance due to RLS has been studied quite well polysomnographically, little is known about the electrophysiological function during daytime. The aim of the present study was to investigate the diurnal quantitative EEG and clinical symptomatology in 33 drug-free RLS patients as compared with age- and sex-matched normal controls. Investigations comprised brain mapping of the vigilance-controlled EEG as well as completion of the Zung Self-Rating Depression Scale, the Zung Self-Rating Anxiety Scale, the Quality of Life Index, the Pittsburgh Sleep Quality Index and the Epworth Sleepiness Scale for evaluation of clinical symptomatology. Statistical analysis demonstrated an increase in absolute delta and absolute and relative alpha-2 power, a decrease in absolute and relative alpha-1 power, an acceleration of the dominant frequency and the alpha centroid, and a slowing of the delta/theta centroid, as well as a non-significant attenuation in total power. These findings are characteristic of dissociated vigilance changes described in depression. Indeed, RLS patients demonstrated significantly higher depression and anxiety scores, lower quality of life and deteriorated sleep quality. The score of the Epworth Sleepiness Scale was not elevated, in contrast to the increased daytime sleepiness observed in other highly prevalent organic sleep disorders (e.g. sleep apnea). In conclusion, daytime EEG mapping revealed neurophysiological correlates of depression in RLS, which was confirmed by self-ratings at the symptomatological level.