Introduction A valid and reliable self-administered scale to measure multidimensional aspects of female sexual function is needed in Japan, as sexual dysfunction is quite common in Japanese women. Aim The aim of this paper is to develop a Japanese translation of the Female Sexual Function Index (FSFI-J), 3-month version, and to measure its psychometric reliability and validity. Methods Following a language validation process and pilot tests, we modified the scale by adding some instructions and answer options. A cross-sectional survey to examine psychometric reliability and validity of FSFI-J was conducted with 126 healthy Japanese women in partnered relationships. Reliability studies on test–retest and on internal consistency were conducted using the intraclass correlation coefficient (ICC) and Cronbach's α coefficient, respectively. A validity study was conducted on aspects of face, construct, concurrent, and discriminant validity. Main Outcome Measures The main outcome is the psychometric reliability and validity of FSFI-J. Results FSFI-J showed high test–retest reliability (ICC > 0.78) and high internal consistency (Cronbach's α > 0.84). In terms of face validity, FSFI-J was found to be understandable and can adequately measure various aspects of female sexual function. Regarding construct validity, exploratory factor analysis of FSFI-J supported a five-factor solution, consisting of desire/arousal, lubrication, orgasm, satisfaction, and pain. This domain structure was identical to that of the original FSFI. Regarding concurrent validity, FSFI-J total score and domain scores showed significant correlations (Pearson's r = −0.613 for total score) with the sexual function domain of the perimenopausal subjective symptom inventory and overall sexual satisfaction as measured by a visual analog scale (Pearson's r = 0.387). For discriminant validity, the regular menstruation group showed significantly higher FSFI-J scores than the menopause group in the total score and all subdomain scores except sexual satisfaction. Conclusions The FSFI-J is a valid and reliable instrument to measure multidimensional aspects of sexual function in healthy Japanese women who are in partnered relationships.

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