Type 1A diabetes (DM1A) is an autoimmune disease that comprises 10% of patients with diabetes mellitus. Its frequency is gradually increasing in countries like Mexico. Patients with DM1A commonly have hypothyroidism, Addison disease, celiac disease and less common diseases such as polyglandular syndrome. These diseases are related to susceptibility genes such as HLA, CTLA-4 and PTPN22, which induce central and peripheral immunologic tolerance. This review article emphasizes the importance of searching other autoimmune diseases in patients with DM1A, to improve their prognosis and quality of life.