In the International Classification of Sleep Disorders(ICSD), REM sleep behavior disorder(RBD) and nightmares are classified as parasomnias usually associated with REM sleep . RBD can be defined as the intermittent absence of REM sleep EMG atonia and the appearance of the elaborate motor activity associated with dream mentation. Bilateral pontine tegmental lesions in cats induce RBD-like behavior, but in human cases, more than 60% are idiopathic. Polysomnograpy shows characteristic findings in REM sleep and treatment with clonazepam is highly effective. With nightmares as long, frightening dream decreasing with age, their persistence or apperance in adults is related with certain drugs, trauma, personality and psychotic episode. Psychotherapy, behavior techniques or medication is used for treatment, but all of nightmares do not require treatment.