REM sleep behaviors were recently described as wild, dream-enacting behaviors during REM sleep with loss of usual atonia on submental muscles. We examined 6 patients (5 M, IF) with characteristic episodes of behavioral manifestations during REM sleep. Polysomnographic data indicate a decrease in first REM latency, an absence of stage 4 NREM, altered phasic motor activity and behavioral episodes during REM sleep even with normal chin muscle atonia. Three patients had Shy-Drager syndrome, 1 olivopontocerebellar atrophy and 2 patients had no neurological disease. The crucial importance of a disinhibited locomotor system during sleep appears to be responsible for this REM parasomnia.