This study reports a case of plasma cell granuloma of the thyroid gland in a 47-year-old woman, presenting with a right subhyoid mass and a previous diagnosis of Hashimoto thyroiditis dating back to 1988, which was made on a subtotal thyroidectomy. Plasma cell granuloma preferentially involves the lung, with only 18 cases of thyroid gland involvement having been reported to date in the English literature. Thyroid plasma cell granuloma preferentially affects women and classically shows a prominent plasma cell infiltrate embedded in a variable degree of fibrous stroma: only 2 of the reported cases exhibited the morphologic features of inflammatory myofibroblastic tumor. These morphologic features may raise problems in the differential diagnosis with other plasma cell-rich disorders, including infectious diseases and auto(dys)immune conditions, including the recently described "IgG4-related sclerosing disease." In view of these considerations, a contemporary diagnostic approach to thyroid plasma cell granuloma is therefore discussed here.