Thyroiditis is inflammation of the thyroid gland in the neck. This inflammation may result in hypothyroidism, when the thyroid produces too few hormones, or hyperthyroidism, when the thyroid produces too many hormones.

Thyroiditis is usually related to a problem with the body's immune system. Antibodies, which are substances made by the immune system to attack and destroy foreign substances in the body, attach to normal thyroid tissue. This process causes the thyroid to function abnormally. This type of thyroiditis is called autoimmune thyroiditis or Hashimoto's thyroiditis. Thyroiditis may also be caused by infection with a virus.

Thyroiditis is treated with medicines.