Fulminant type 1 diabetes mellitus (T1DM) and drug hypersensitivity syndrome (DHS) are rare and life-threatening diseases. Fulminant T1DM may develop after DHS with only few previous case reports and the possible role of human herpes virus 6 (HHV-6) infection was indicated in the pathogenesis.We here presents three cases of fulminant T1DM developed shortly after the diagnosis of drug-induced hypersensitivity syndrome. The offending drugs were identified as Cefadroxil, cefuroxime and phenylbutazone respectively. All of them were treated with high dose of glucocorticoids when hyperglycemia symptoms occurred abruptly with rapid progression to ketoacidosis. In terms of immunological parameters, one patient was positive for both GADA and ZnT8A, and had haplotypes of DQA1*0601-DQB1*0301 / DQA1*0601-DQB1*0301. The second one had positive GADA and DQA1*0102-DQB1*0601 / DQA1*05-DQB1*0201 haplotypes. The third patient was negative for all autoantibodies tested and had haplotypes of DQA1*03-DQB1*0302 / DQA1*03-DQB1*0303. Although HHV-6 virus antibodies were not detected in these patients, we found herpes simplex virus type 1 IgM antibodies (HSV1 IgM) positive in one and Coxsackie virus IgM antibodies (CVB IgM) positive in another patient. Our understanding of the pathogenesis of fulminant T1DM will be improved if the relationship among DHS, glucocorticoids and virus infection can be clarified.More attention shoule be given to this novel and serious complication of patients with DHS.