Introduction: Malignant struma ovarii is a rare neoplasm. It is usually asymptomatic and not commonly diagnosed preoperatively. In addition, there is currently no established diagnostic and therapeutic approach for malignant struma ovarii. Case Report: A 66-year-old asymptomatic female was referred to our hospital. Computed tomography showed the presence of a well-defined mass with enhancement in the internal and peripheral areas. The patient underwent total abdominal hysterectomy, bilateral salpingo-oophorectomy, and partial omentectomy. Histopathology revealed the presence of a papillary thyroid carcinoma arising from a 2.5-cm-diameter struma ovarii (malignant struma ovarii). According to the criteria of the International Federation of Gynecology and Obstetrics, the patient had stage IA disease. Subsequently, she underwent a thyroid scan with normal findings. At the 3-month follow-up, the patient was alive, in good clinical condition, and disease free. Conclusion: In this report, we present the smallest malignant struma ovarii reported so far in the literature. Because of the rarity of these tumors and the lack of firm prognostic factors, the treatment decision should be customized for each patient according to the pathological and clinical parameters.
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