Malignant struma ovarii is a rare disease; only a few cases are well documented in the literature. Thus, the overall prognosis and modalities of treatment are still somewhat controversial. In this article, the authors report a case of malignant struma ovarii discovered 4 years after ovariectomy after metastasis to the lungs and bones. Review of the pathology of the ovarian struma did not reveal the classic criteria of malignancy, there were, however, many features considered to be atypical and thus suspicious. The patient was treated by total thyroidectomy followed by repetitive doses of 131I. However, because of difficulties in increasing the level of endogenous thyrotropin (TSH) because of functional thyroid metastases in such an advanced disease, recombinant human thyrotropin (rhTSH; Thyrogen, thyrotropin alpha, Genzyme Corporation, Cambridge, MA) was used before administration of radioiodine. With this therapeutic protocol, the patient is still clinically stable 2 years after diagnosis.