This case report documents the treatment of a female patient, 37 years 6 months of age, with a Class II open bite malocclusion with severe osteoarthritis of the temporomandibular joint associated with Hashimoto disease, a chronic inflammatory disease of the thyroid in which autoimmune factors play a prominent role. The simultaneous treatment of both pathologies (malocclusion and thyroiditis) led to the cessation of pain and dysfunctional symptoms in both temporomandibular joints. World J Orthod 2004;5:254–259.