Plasma cell granuloma (PCG) is a rare, benign inflammatory tumor composed of myofibroblasts, abundant plasma cells, and lymphocytes combined with collagen. A thyroid localization of PCG is extremely rare, and surgical therapy is indicated. We report the case of a 35-yr-old woman with a thyroid PCG, associated with Hashimoto's thyroiditis, that was responsible for tracheal compression. Surgery was performed, but the thyroid could not be removed because of the fibrotic process. The patient was treated with corticosteroids and immunosuppressive therapy. Dyspnea and dysphagia improved within 1 month, whereas thyroid volume returned to normal within 3 yr. We also review other reports of thyroid PCG in the literature and discuss the differential diagnosis and treatment. Although the use of immunosuppressive therapy has never been reported for thyroid PCG until now, this treatment may represent a good alternative to surgery in life-threatening, unresectable PCG.