Autoimmune thyroid disease (AITD) including Graves' disease, Hashimoto's thyroiditis, and idiopathic hypothyroidism (atrophic Hashimoto's thyroiditis) is of vital concern to the dermatologist. This article reviews the cutaneous manifestations of Graves' disease and Hashimoto's thyroiditis. Recognition of dermatologic manifestations of AITD may alert practitioners to investigate for these disorders. The immune response involved in the pathogenesis of AITD is detailed. Current understanding of the role of genetic and environmental factors, antigens, and apoptosis are elaborated. The future holds exciting insight into the etiology, pathogenesis, and treatment of AITD. (J Am Acad Dermatol 2003;48:641-59.) Learning objective: At the conclusion of this learning activity, participants should better understand how to evaluate and treat patients with dermatologic manifestations of autoimmune thyroid disease. Participants should also gain insight into the pathogenesis of these disorders, including the role of genetic and environmental factors, antigens, and apoptosis.