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STUDY OBJECTIVES To evaluate the prevalence and clinical characteristics of isolated REM sleep behavior disorder (iRBD) among a general population of elderly Japanese people. METHODS This epidemiological study targeted 2714 elderly residents (76.0±8.0 yr, 52.9% female) of a rural community. Questionnaires including the REM sleep behavior disorder single question and demographic information were distributed. All respondents with the question positive were interviewed by telephone. Respondents suspected of having iRBD proceeded to face-to-face interviews and underwent video-polysomnography and neurological / neuropsychological examination. These results were compared to those of previously diagnosed clinical iRBD patients in our sleep clinic. RESULTS Of 1464 respondents to the questionnaire, 18 respondents were diagnosed as iRBD (1.23 [0.66-1.79]%), including 8 respondents who satisfied diagnostic criteria with REM sleep without atonia (RWA) above the cut-off value (0.54 [0.17-0.92]%) and 10 respondents who had clear dream enactment behaviors but not RWA above the cut-off (provisionally diagnosed iRBD; p-iRBD) (0.69 [0.26-1.11]%). Severity of RBD and RWA of the population-based iRBD were compatible with those of the clinical iRBD. Half of the population-based iRBD showed orthostatic hypotension and they showed lower olfactory function than population-based p-iRBD and non-RBD. However, their olfactory and cognitive functions were higher than those in the clinical iRBD patients. CONCLUSIONS Prevalence of iRBD in Japanese elderly people was comparable with the rate reported from other countries. Population-based iRBD / p-iRBD showed lower neurodegenerative loading than clinical iRBD in spite of comparable disease duration of RBD, that may indicate their lower risk of future neurodegeneration.