OBJECTIVES: Rapid eye movement (REM) sleep behavior disorder (RBD) is a parasomnia manifested by vivid dreams associated with complex motor behavior during REM sleep. It was originally described as a parasomnia in older men, however it is now recognized as a disorder of all ages and both sexes. We determine clinical characteristics of young age RBD patients who visited single sleep center in Korea. METHODS: This is a retrospective chart review of RBD patients visiting single sleep center from August, 2003 to August, 2014. Patients with history of RBD were evaluated with overnight polysomnography (PSG). The PSG results were compared between young (<40 years old) and elderly (40 years or older). RESULTS: The total of 149 patients (young RBD: n=22, 14.8%, elderly RBD: n=127, 85.2%) were included. Mean age upon diagnosis were 24.97+/-7.42 years (male: n=17, 77.3%) for young age RBD, and 64.40+/-8.73 years (male: n=82, 64.6%) for elderly RBD patients. PSG results reveled young age RBD patients had longer total sleep time (416.16+/-44.19, 345.73+/-78.03, p<0.001), higher sleep efficiency (87.60+/-6.90, 76.85+/-14.07, p<0.001), less arousal index (17.85+/-20.81, 23.14+/-12.15, p<0.001). Three patients in young age RBD group were also diagnosed with narcolepsy. CONCLUSIONS: This is the first study to evaluate PSG findings in young age RBD in Korean. The young age RBD sleep longer and better, with less arousal. Further on they have associated with sleep talking and walking, and narcolepsy. While few previous reports indicated association with medication use, our young age population was not related to medication effects.