Struma ovarii belongs to the group of monodermal and highly specialized teratomas and comprises less than 5% of mature teratomas. Thyroid tissue is present exclusively or predominantly. Malignant transformation in struma ovarii is uncommon, and when present, it exhibits a follicular pattern most of the times. Three patients with the diagnosis of struma ovarii are presented herein. Two of them had a unilateral adnexal mass with ascites in one case. Total abdominal hysterectomy with bilateral salpingo-oophorectomy and omentectomy were carried out in both patients. In both patients thyroid hormonal status was normal pre and postoperatively. The third patient had a histology compatible with follicular carcinoma of the thyroid tissue of struma ovarii; strumal carcinoid was also present. Postoperatively monochemotherapy with etoposide was administered for 6 cycles every 3 weeks. Thyroid hormones and thyroid ultrasonography (US) were also normal in this patient. Surgical management is the treatment of choice for struma ovarii which also represents a preventive measure for possible future malignant transformation.