Type 1 diabetes is characterized by insulin deficiency due to destruction of pancreatic beta-cells. Patients with type 1 diabetes, with no islet autoantibodies, but with acute onset, are classified as having idiopathic of type 1B diabetes. In 2000, this diabetes subtype was described and named "fulminant type 1 diabetes". The clinical characteristics of this subtype of type 1 diabetes are: a remarkably abrupt onset of disease, very short(<1 week) duration of diabetic symptoms, acidosis at diagnosis, negative status of islet-related autoantibodies, virtually no C-peptide secretion(<10 microgram/day in urine), a near normal HbA1c level and an elevated serum pancreatic enzyme level. Since 1988, several cases showing the clinical characteristics of fulminant type diabetes have been reported, with this subtype accounting for approximately 20% of Japanese type 1 diabetes. There have been few cases of fulminant type 1 diabetes in Korea. Herein, our experience of two cases of fulminant type 1 diabetes is reported, with a review of the literature.