Abstract In previous studies it has been demonstrated that during sleep healthy subjects with consistent left- or right- handedness perform about two thirds of their movements with the non-dominant hand. We examined the motor activity during waking and sleep of 13 medicated hallucinating schizophrenic patients without motor side effects and 17 control subjects using bilateral wrist actometry during two nights. Five of the patients were also monitored by continuous infrared video recording and by the Static Charge Sensitive Bed method during the movement recording nights. Lateralization to the non-dominant side during nocturnal low activity period or sleep was absent in the schizophrenic group, in which the dominant hand remained more active. This was not due to movement excess. The difference in lateralization between the controls and the patients should be considered a preliminary finding until replicated. It suggests abnormal laterality of arousal, attention or movement system during sleep in schizophrenia. It may imply abnormality in the sleep dependent modification of attentive behavior, or it may be explained by the lateralized effects of neuroleptic medication.