Even though autoimmune thyroiditis is considered as the most emblematic type of organ-specific autoimmune disorder of autoimmunity, autoimmune thyroid diseases can be associated with other autoimmune endocrine failures or non-endocrine diseases (namely vitiligo, pernicious anemia, myasthenia gravis, autoimmune gastritis, celiac disease, hepatitis). Thyroid disorders, which are the most frequent expression of adult polyendocrine syndrome type 2, occur concomitantly with or secondarily to insulinodependent diabetes, premature ovarian failure, Addison's disease (Schmidt syndrome, or Carpenter syndrome if associated with diabetes). Testicular failure and hypoparathyroidism are unusual. The disease is polygenic and multifactorial. Disorders of thyroid autoimmunity are, surprisingly, very rare in polyendocrine syndrome type 1 (or APECED) beginning during childhood. They are related to mutations of the AIRE gene that encodes for a transcriptional factor implicated in central and peripheral immune tolerance. Hypothyroidism can also be observed in the very rare IPEX and POEMS syndromes.