Eiji KawasakiTaro MaruyamaAkihisa ImagawaTakuya AwataHiroshi Ikegami • Yasuko UchigataHaruhiko OsawaYumiko KawabataTetsuro KobayashiAkira Shimada • Ikki ShimizuKazuma TakahashiMasao NagataHideichi MakinoToshiaki Hanafusa

Type 1 diabetes is a disease characterized by destruction of pancreatic b cells, which leads to absolute deficiency of insulin secretion. Depending on the manner of onset and progression, it is classified as fulminant, acute- onset, or slowly progressive type 1 diabetes. Here, we propose the diagnostic criteria for acute-onset type 1 dia- betes mellitus. Among the patients who developed diabetic ketosis or ketoacidosis within 3 months after the onset of hyperglycemic symptoms and need insulin treatment con- tinuously after the diagnosis of diabetes, patients with anti- islet autoantibodies are diagnosed with ''acute-onset type 1 diabetes mellitus (autoimmune)''. On the other hand, those whose endogenous insulin secretion is exhausted (fasting serum C peptide immunoreactivity (CPR) \ 0.6 ng/ml) without verifiable anti-islet autoantibodies are diagnosed simply with ''acute-onset type 1 diabetes mellitus''. Patients should be reevaluated after certain periods in case their statuses of anti-islet autoantibodies and/or endoge- nous insulin secretory capacity is unknown.