Autoimmune problems can affect virtually any part of the body, and the thyroid gland is no exception. When an autoimmune problem attacks the thyroid, the result is Hashimoto's thyroiditis. Today, Hashimoto's is the most common form of thyroiditis and the leading cause of hypothyroidism in the United States. In this chapter, you'll learn about causes, symptoms, diagnosis, and treatment of Hashimoto's, as well as the other forms of thyroiditis.