OBJECTIVE The aim of this study was to investigate the involvement of temporo-occipital regions in the pathophysiology of autistic spectrum disorders (ASD) by using REM sleep and waking EEG. METHODS The EEG recordings of 9 persons with ASD and 8 control participants were recorded using a 12-electrode montage. Spectral analysis (0.75-19.75 Hz) was performed on EEG activity recorded upon two activated states: REM sleep and wakefulness. RESULTS During REM sleep, persons with ASD showed a selective, significantly lower absolute beta (13.0-19.75 Hz) spectral amplitude over the primary (O(1), O(2)) and associative (T(5), T(6)) cortical visual areas compared to controls. Persons with ASD showed significantly higher absolute theta (4.0-7.75 Hz) spectral amplitude over the left frontal pole region (Fp1) compared to controls during evening wakefulness, but not during morning wakefulness. CONCLUSIONS The results of waking EEG are consistent with previously reported observations of neuropsychological signs of frontal atypicalities in ASD; results from REM sleep are the first EEG evidence to support the hypothesis of abnormal visuoperceptual functioning in ASD. Altogether, these results point toward atypical thalamo-cortical mechanisms subserving the neural processing of information in ASD.