OBJECTIVE: To classify type 1 diabetic females with bulimia nervosa (BN) by type of inappropriate compensatory behavior in order to prevent weight gain (ICB) and to investigate the group differences. RESEARCH DESIGN AND METHODS: Type 1 diabetic females with BN, diagnosed by structured diagnostic interview based on DSM-IV (Diagnostic and Statistical Manual of Mental Disorders, 4th ed.) criteria, were classified by type of ICB as follows: 1) only severe insulin omission as an ICB (BN-I) (n = 22), 2) both severe insulin omission and self-induced vomiting and/or laxative abuse (BN-IP) (n = 22), or 3) no insulin omission but another ICB (BN-NI) (n = 11). The clinical characteristics of these three groups and a binge-eating disorder (BED) group (n = 24) were compared. RESULTS: The BN-IP and BN-I groups had the highest HbA(1c) levels. The BN-IP group had the highest rates of diabetic neuropathy, retinopathy, and nephropathy. The BN-NI group had the second highest rates of neuropathy and retinopathy. The BN-IP group had the highest frequencies of diabetes- and ketoacidosis-related hospital admissions, and the BN-I group had the second highest frequencies. The BN-NI group showed the highest scores on psychological tests related to depression, anxiety, eating disorder psychopathology, and perfectionism. The BN-NI group had the highest rate of history of visits to a psychiatrist, and the BN-IP group had the second highest history. CONCLUSIONS: Type 1 diabetic females with BN seem not to be homogenous and can be classified into three distinctive subgroups by type of ICB. Individuals with BN-IP had the most severe problems with both medical and psychological/behavioral aspects. Individuals with BN-NI manifested the highest psychological distress. The BN-I group had comparatively mild distress despite having the poorest metabolic control. Each BN group manifested more severe pathology than the BED group.