The effect of sleep on the involuntary movements or dyskinesias in Parkinson's disease, Huntington's disease, primary and secondary torsion dystonia, and Gilles de la Tourette syndrome was studied in a total of 52 patients and 10 normal subjects using video electroencephalographic telemetry. Movements typical of the wake pattern were seen occasionally during unequivocal sleep in all but two completed studies, and in each condition reappeared under similar circumstances. The movements were most likely to occur after awakenings or lightenings of sleep, or in stage one sleep. The movements were very rare during the deeper phases of sleep. Those movements that occurred during sleep without awakenings were usually preceded by arousal phenomena and, rarely, by sleep spindles or slow waves. The control group showed normal "semipurposeful" movements under the same conditions during sleep. The rare appearance of the different dyskinesias and normal movements under similar circumstances during sleep could be a result of common effects on the generator systems or changes in the excitability of the final common motor pathway.