Autoimmune thyroid disease is common in patients with either systemic lupus erythematosus (SLE) or Sjögren's syndrome (SS); however, whether the risk is greater than in well matched controls is not clear. Antinuclear antibodies are found in the sera of patients with autoimmune thyroid disease, but there is no evidence of autoantibodies binding antigens characteristic of SLE or SS. Autoantibodies to thyroid antigens and overt autoimmune thyroid disease are common in patients with SLE or SS. However, in SLE patients there is little or no increased risk of autoimmune thyroid disease compared to an age and sex matched population. Patients with SS are likely to be at increased risk of thyroid disease, but those with autoimmune thyroid disease are not at special risk of SS. This difference can be explained if SS is considered to be an autoimmune epitheliitis that targets polarized epithelia, including the thyroid.