Enomoto K, et al. - Researchers sought to validate the psychometric properties of two versions of Athens Insomnia Scale (AIS), the AIS-8 (full version) and the AIS-5 (brief version). Among chronic pain patients, validation was achieved by confirming factor structure by confirmatory factor analysis, internal consistency by Cronbach’s a, test–retest reliability using with interclass correlation coefficients, known-group validity, concurrent validity, and cut-off values by receiver operating characteristic analysis. In this study, a 2-factor model of the AIS-8 and 1-factor model of the AIS-5 showed a good fit. Both adequate internal consistency and test–retest reliability were demonstrated by the AIS, confirming that the AIS-8 and AIS-5 are adequately reliable and valid in chronic pain patients.