The aim of this study was to evaluate the psychometric properties of the Korean version of the European Organization for Research and Treatment of Cancer Breast-Cancer-Specific Quality of Life Questionnaire (EORTC QLQ-BR23). A total of 153 patients with breast cancer and 153 normal subjects completed three questionnaires of the Korean version of the EORTC QLQ-BR23. Multitrait scaling analyses demonstrated that all scales met multidimensional conceptualization criteria in terms of convergence and discrimination validity. Cronbach's alpha coefficients for five multiple-item scales were greater than 0.70 (range, 0.72-0.91). In known-group comparisons, there were marked group differences between patients differing in disease stage. In breast cancer patients, performance on the questionnaires was in the expected direction for almost all functioning and symptom scores. In addition, comparison between the patient and control groups showed that almost all variables discriminated between patients and normal individuals. In conclusion, the Korean version of the EORTC QLQ-BR23 was found to be a reliable and valid measure of quality of life in breast cancer patients, indicating that it should be used in clinical and epidemiological cancer research.