Type 1 diabetes (T1D) comprises all forms of autoimmune-mediated and idiopathic beta-cell destruction leading to absolute insulin deficiency. The etiological heterogeneity of T1D has been recognized for the last decades, but it has been divided into only two subtypes so far: autoimmune (T1D)A and non-autoimmune (T1D)B mediated. Polygenic T1DA (isolated or associated to other autoimmune diseases) is the most prevalent type of T1D. T1DA might be part of rare monogenic syndromes related to mutations in the autoimmune regulator gene (AIRE) and FOXp3. Non-autoimmune forms of T1D correspond to approximately 4 to 7% of newly diagnosed T1D and include T1DB, as well as other types of atypical diabetes, for example fulminant type 1 diabetes and adult ketosis-prone diabetes. A new expression of diabetes in young with insulin resistance and obesity, along with the presence of pancreatic autoimmunity markers, namely auto-antibodies to islet cell antigens, is called double diabetes (DD), T1DA plus type 2 diabetes. Evidence has been collected concerning the potential effect of obesity-linked cytokines in amplifying the autoimmune response in DD. Therefore all these issues are presented and discussed in this review as the concept of heterogeneity of Type 1 Diabetes.