After removal of an ovarian mass in a 43-year-old woman, a struma ovarii was diagnosed. Within this teratoma, a papillary thyroid cancer was found. The tumor was negative for BRAF, NRAS, KRAS, PIK3CA and c-KIT mutations on molecular analysis. Thyroid function and morphology were normal. Thyroidectomy, L-T4 TSH-suppressive therapy and rhTSH-induced radioiodine ablation were performed. So far, the follow-up has been favorable. This is the first case of thyroid cancer in a struma ovarii in which mutations of PIK3CA exons 9 and 20, and c-KIT exons 9, 11 and 13 have been evaluated and the third in which ablation has been performed under rhTSH. The prognosis of patients with thyroid cancer in a struma ovarii is generally poor. In our patient, as in those who undergo ablative radioactive iodine therapy, this was not the case.