Although it is well-known that autoimmune thyroid diseases are more common in most of the autoimmune connective tissue diseases, the relationship between autoinflammatory diseases and autoimmune thyroid diseases has not well-evaluated yet and still remains unclear. The aim of this study was to investigate the frequency of autoimmune diseases of the thyroid gland and to evaluate thyroid function tests in children with familial Mediterranean fever. Thyroxine, thyroid-stimulating hormone, and thyroid autoimmune markers such as thyroid peroxidase and thyroglobulin antibodies, and thyroid ultrasound findings of 133 patients with familial Mediterranean fever and 70 healthy controls were evaluated. Serum levels of thyroid-stimulating hormone, free thyroxine, and thyroid autoimmunity markers were similar in patients with familial Mediterranean fever compared with healthy controls. There was no relationship between the duration of the disease and thyroid-stimulating hormone, free thyroxine, anti-thyroid peroxidase, and anti-thyroglobulin levels. This study revealed that incidence of thyroid dysfunction and autoimmunity is not increased in patients with familial Mediterranean fever. In conclusion, routine screening of serum thyroid function tests and thyroid antibody levels is not required in patients with familial Mediterranean fever in the absence of clinical symptoms or family history.