Autoimmune polyendocrinopathies are rare diseases characterized by the coexistence of at least two endocrine diseases linked to an autoimmune mechanism, however sometimes are associated with non-endocrine autoimmune diseases. They are divided into two main subgroups: autoimmune polyendocrinopathy type I and polyendocrinopathies type II-IV. We report a case of a 53-year-old female patient followed for 2 years for Hashimoto's thyroiditis. On admission, she was complaining of polyuropolydipsic syndrome, asthenia, weight loss, abdominal pain and vomiting. The clinical examination noted a dehydrated patient in poor general condition, without fever, tachycardic at 104 beats/min, and polypneic at 24 cycles/min. Laboratory tests revealed hyperglycemia (4.7 g/l), glucosuria, acetonuria, anti-GAD>2000 UI/l antibody, normal TSH. The 8-hour cortisol level and anti-21 hydroxylase antibodies level were normal. In this context, the patient was diagnosed with diabetes type 1 associated with Hashimoto's thyroiditis (autoimmune polyendocrinopathy type III). In conclusion, the autoimmune polyendocrinopathy type III is a rare syndrome, predominantly affecting females. In our patient's case, the initial presentation of the disease was dominated by the autoimmune thyroiditis, which is the most frequent endocrine autoimmunity diagnosed in adults with polyglandular autoimmune syndrome. Therefore, the recommended treatment is based on hormonal substitution.