ObjectiveTo explore the clinical features of fulminant type 1 diabetes mellitus (FT1DM).MethodsThe clinical data of 6 patients with FT1DM who were hospitalized in Jinshan Hospital of Fudan University from April 2020 to August 2024 were retrospectively analyzed. Their data were compared with that of 30 patients diagnosed with non-fulminant type 1 diabetes mellitus (NFT1DM) and diabetic ketosis or diabetic ketoacidosis (DKA) who were admitted to the hospital during the same period. The clinical characteristics of FT1DM were summarized.ResultsAll 6 patients with FT1DM were male, with a disease course of 2.00 (1.75, 4.00) d. Three cases exhibited a history of prior infection, four tested positive for glutamic acid decarboxylase antibody (GADA), and five developed severe DKA. The glycated hemoglobin A_1C (HbA_1C) was (6.30±0.67)%, fasting C-peptide (FCP) was 0.07 (0.03, 0.15) ng/mL, 2-hour postprandial C-peptide (2h-CP) was 0.09 (0.03, 0.16) ng/mL. At discharge, all 6 patients received 4-injection insulin regimen, with a dose (0.69±0.15) U·kg^-1·d^-1. The body mass index (BMI), blood glucose/HbA_1C, blood potassium/HbA_1C, fasting plasma glucose (FPG), 2-hour postprandial plasma glucose (2h-PG), high-sensitivity C-reactive protein (hs-CRP), alanine aminotransferase (ALT), serum creatinine, and blood potassium levels in the FT1DM group were higher than those in the NFT1DM group (P<0.05), while HbA_1C and glycated albumin (GA) levels were lower than NFT1DM group (P<0.05).ConclusionsFT1DM usually presents with an acute onset of DKA, may be accompanied by a history of preceding infection, and GADA can be positive. Patients with FT1DM have elevated blood glucose/HbA_1C, blood potassium/HbA_1C, FPG, 2h-PG, hs-CRP, ALT, serum creatinine, blood potassium levels, and require insulin therapy, while the HbA_1C and GA levels are lower.