A mildly dyslexic boy of 11 years, with no neurological deficit or history of epileptic seizures, had marked hypersomnia for 2 years, which was most pronounced in the morning hours. Repeated EEG studies and power spectral analysis revealed simultaneous posterior alpha rhythm and sleep patterns (spindles, vertex waves, K complexes) over vertex and frontocentral regions, while the patient was behaviorally awake. Bilateral synchronous anterior spikes were frequently noted in association with sleep patterns. A polysomnogram over 24 h confirmed excessive sleep, night and day (especially morning hours) and there was evidence of a large REM sleep percentage (on EMG and EOG basis) while the EEG had predominantly non-REM sleep patterns. Special neurotransmitter studies were performed in view of a presumed disturbance affecting the neurobiochemical sleep regulation. These studies were based on CSF metabolite levels and provided evidence for a high serotonin metabolite (5HIAA) level. It is tempting to hypothesize that the biochemical disturbance has led to encroachment of non-REM sleep patterns on both wakefulness and REM sleep. Further discussion deals with the bilateral-synchronous spike activity and its relationship to arousal patterns in sleep.