Autoimmune thyroiditis of the Hashimoto type progresses insidiously in most patients and in the long term leads to destruction of the thyroid gland resulting in hypothyroidism. However, there are also phases with passive hyperthyroidism (hashitoxicosis). The disease can occur at any age, but is more common in middle and older adulthood. Women are affected much more frequently than men. Treatment with thyroid hormones allows those affected to lead a normal life.