Abstract
Down's syndrome is the most common genetic disorder. It is well established that there is an increased risk of autoimmune endocrine diseases in Down's syndrome. Defect of a gene located on chromosome 21q22.3 causes autoimmune polyglandular syndrome type 1 and this might be related with susceptibility to autoimmune diseases in patients with Down's syndrome. We reported a 20-year-old male with Down's syndrome who was brought to emergency room by his family and had a diagnose of diabetic ketoacidosis and Graves' disease. Underlying mechanisms in co-existing of autoimmune diseases in Down's syndrome, management of such patients and the importance of making the family to be aware of the symptoms of possible subsequent components of the autoimmune polyglandular syndrome are discussed.