OBJECTIVE: The purpose of this study was to compare the Diagnostic and Statistical Manual of Mental Disorders, fourth edition (DSM-IV) and the proposed Diagnostic and Statistical Manual of Mental Disorders, fifth edition (DSM-5) diagnostic criteria in terms of the number of cases of eating disorder not otherwise specified (EDNOS) and to see which diagnostic system can effectively capture variance in psychiatric symptoms in a Japanese sample. METHOD: One thousand and twenty-nine women with an eating disorder (ED) participated in this study. Assessment methods included structured clinical interviews and administration of the Eating Attitudes Test and the Eating Disorder Inventory. RESULTS: Relaxing the diagnostic criteria for anorexia nervosa and bulimia nervosa and recognizing binge ED decreased the proportion of EDNOS (from 45.1% to 26.1%). The DSM-5 categorization of patients was better able to capture variance in psychopathology scales. CONCLUSIONS: The proposed revisions to EDs in the DSM-5 partially reduced reliance on EDNOS. The DSM-5 may differentiate ED groups more effectively than the DSM-IV.