Struma ovarii is a monodermal variant of ovarian teratoma. Thyroid-type carcinoma arising in struma ovarii is rare. The most common type is papillary carcinoma, followed by typical follicular carcinoma, and the new entity of follicular carcinoma-highly differentiated follicular carcinoma of ovarian origin; other forms occur rarely. Consensus on the surgical and postoperative treatment of patients with thyroid-type carcinoma arising in struma ovarii has not been reached. Surgical treatment ranges from total abdominal hysterectomy, plus bilateral salpingo-oophorectomy with omentectomy, to conservative surgery, involving unilateral oophorectomy or strumectomy (cystectomy) for fertility preservation. Adjuvant therapy includes external radiotherapy, chemotherapy, thyroidectomy, and radioactive iodine ablation. Thyroid-type carcinomas arising in struma ovarii, especially the newly recognized entity-highly differentiated follicular carcinoma of ovarian origin-have a favorable prognosis.