Rosai-Dorfman disease (RDD), otherwise known as sinus histiocytosis with massive lymphadenopathy, is a rare histiocytic syndrome of unknown etiology, dominated by histiocytic and lymphocytic infiltration of enlarged lymph nodes. Thyroid involvement is rare and its impact unknown. We report a case of RDD involving the thyroid, initially diagnosed and managed as anaplastic carcinoma, and review the literature for previously reported cases of thyroid involvement. A 71-year-old woman sought further evaluation after treatment elsewhere for a 4-month history of a rapidly enlarging goiter causing local compression. Pathology was reported to show anaplastic thyroid carcinoma with prominent histiocytic infiltration. On review, we found characteristic features of RDD within the thyroid and cervical lymph nodes. The patient showed serologic evidence of autoimmune thyroid disease. Two years after thyroidectomy, there was no evidence of recurrent disease. We have identified only three previously reported cases of RDD involving the thyroid, all of them in women. In all cases, the patient has survived without evidence of disease progression, suggesting that thyroid involvement may not change the generally good prognosis of RDD. The description of autoimmune thyroid disease in our case and in two of the three previously reported cases, suggests a link with autoimmune thyroid disease.