What Is Hashimoto Disease Hashimoto Disease is an autoimmune disorder in which your immune system attacks your thyroid gland. As a result of this attack, the thyroid becomes inflamed and is unable produce adequate levels of thyroid hormones. This hormone deficiency results in hypothyroidism, or what many people refer to as underactive or low thyroid. in Public bookmarkswith diagnosisdiseasehashimotohashitoxicosisisshashimotosymptomwhat