Plasma cell granuloma of the thyroid is a rare tumor-like lesion formed by a localized proliferation of inflammatory cells, supported by a stroma of fibrous tissue. Few cases have been previously reported in the medical literature. We report a new case of a 41-year-old man presenting a goiter with primary hypothyroidism (thyroid-stimulating hormone, 70 mIU/L; free thyroxine, < 0.01 pmol/L; triiodothyronine, 0.66 nmol/L) and elevation of thyroid antibodies. Several fine-needle aspiration biopsies of the thyroid were fruitless and total thyroidectomy was performed. Histologic and immunohistochemical study demonstrated the polyclonal nature of the cells and yielded a diagnosis of plasma cell granuloma. Histologic findings of Hashimoto thyroiditis were present too.