An understanding of health-related quality of life (HRQOL) is of utmost importance in both oncological and esthetic breast surgery. The BREAST-Q is a patient-reported outcome (PRO) measure that investigates HRQOL and patient satisfaction before and after breast surgery. The aim of this study was to develop a Japanese version of the BREAST-Q including the mastectomy module, the reconstruction module, the augmentation module and the reduction/mastopexy module, and to assess the psychometric properties of the mastectomy module among Japanese women.The Japanese version of the BREAST-Q was developed through forward translation, backward translation and patient testing. Traditional psychometric testing of the mastectomy module was administered to 45 post-mastectomy patients.The mastectomy, reconstruction, augmentation and reduction/mastopexy modules were formally developed into Japanese. Despite cultural difference between Japanese women and original target population, the contents were considered to be valid among Japanese woman. With the exception of the sexual well-being subscale, good reliability and validity were evident for the mastectomy module (Test-retest reliability 0.76-0.95, Chronbach's alpha coefficient 0.77-0.98).The BREAST-Q Japanese version is a useful PRO measure for investigating the impact of breast surgery on HRQOL and patient satisfaction. Further validation in younger Japanese women is needed to determine the usefulness of the sexual well-being subscale.