Malignant struma ovarii is an extremely rare tumor. Two new cases are described and current perspectives provided. Both cases are examples of the mixed form of the disease, and both were treated by surgery alone. One patient underwent total hysterectomy and bilateral salpingo‐oophorectomy; the other had unilateral salpingo‐oophorectomy. Both patients remained free of recurrent disease at 20 and 33 months from diagnosis. The controversies relating to therapy and diagnosis are discussed in detail.