Recently, a novel subtype of type 1 diabetes, so-called fulminant type 1 diabetes, has been proposed. One of the characteristics of this subtype is the absence of detectable "islet-associated" autoantibody, so it was originally proposed as being "nonautoimmune-mediated"; however, it has not yet been concluded whether autoimmunity is involved. We have previously shown that serum interferon-inducible protein-10 and glutamic acid decarboxylase-reactive CD4(+) interferon-gamma-producing cells in the peripheral blood are good markers for T cell-mediated autoimmunity in type 1 diabetes. Here, we report two cases of fulminant type 1 diabetes in which these markers were detected and in which the involvement of islet-associated autoimmunity is suggested.