We report a 69 years old male with a parkinsonian syndrome and a 50 years old female without neurological problems who showed violent behavior during REM sleep. Polysomnography showed that both had tonic or phasic muscular activity during REM sleep and a REM sleep behavior disorder was diagnosed. Clonazepam was used in both, with good clinical response. This condition is frequently unrecognized and confused with nightmares, nocturnal delirium or other parasomnias