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Background: This study aimed to provide a psychometric evaluation of the Japanese version of the Patient Assessment of Constipation Quality of Life questionnaire (JPAC-QOL)., Methods: Data for scoring were collected prospectively from patients with constipation who visited our center from 2008 to 2010, and analyzed retrospectively. Reliability of the JPAC-QOL was evaluated using Cronbach's alpha to calculate internal consistency, and a test-retest study was performed to evaluate reproducibility. For concurrent validity assessment, the JPAC-QOL scores were compared with Constipation Scoring System (CSS) scores. In assessing responsiveness, the JPAC-QOL scores before and after treatments were compared in patients whose modified CSS (mCSS) scores decreased by >50 %., Results: Internal consistency was assessed in 295 patients (165 women; mean age 67.0 years). Cronbach's alpha was >0.7 for the overall score and all four subscales, showing a strong internal consistency. The intraclass correlations for the 145 patients available for the test-retest study were >0.7 for the overall score and for all subscales except satisfaction. The JPAC-QOL scores were significantly associated with the CSS scores in 284 patients, demonstrating concurrent validity in all four subscales and the overall score. The mean JPAC-QOL score improved significantly after treatment in the 72 patients whose mCSS scores decreased by >50 %, indicating good responsiveness in all four subscales and in the overall score., Conclusions: Our study data confirmed the validity and reliability of the JPAC-QOL and demonstrated it ready for use in evaluating the symptom-specific QOL in Japanese patients with constipation.