Background: The Personal Outcomes Scale is a measurement tool to examine quality of life among persons with intellectual disability. This paper addressed the validity and reliability of the Japanese version of the scale using both self-reports and reports of others. Method: Data were collected from 128 people with intellectual disability (90 men and 38 women; M[subscript age] = 37.19 ± 11.90 (range = 19-69) years) and 27 support workers. Reliability was examined by Cronbach's alpha coefficients, inter-respondent reliability coefficients, and test-retest reliability. Validity was examined by construct validity and criteria-related validity. Results: Self- and other-reported versions showed adequate internal consistency ([alpha] = 0.79); however, some domains had relatively low internal consistency. Validity tests showed weak to moderate correlations between the total score and the domain scores in both versions. Conclusions: The scale is reliable overall; however, cultural aspects should be considered to bolster its reliability for practical application.