Objective: To evaluate the clinical characteristics of struma ovarii. Methods: Twenty-five cases of struma ovarii were reviewed retrospectively from June 1994 to April 2007. The presenting clinical, radiologic, and pathologic features of the patients were reviewed. Results: The mean age of the patients in this study was 45.3 years. The majority was of premenopausal status. Sixteen patients had clinical symptoms such as low abdominal pain, palpable abdominal mass and vaginal bleeding. Although one patient had an abnormal thyroid function test, the laboratory findings normalized after operative treatment. CA-125 levels were elevated in 6 cases. Diagnosis by preoperative imaging studies were 8 dermoid cysts, while only 3 cases were diagnosed as struma ovarii. There were 4 cases of malignant struma ovarii, and no patients with recurrent disease. Conclusion: Struma ovarii is a rare tumor. The presented clinical, laboratory and radiological findings of patients are very diverse. The diagnosis was confirmed by pathologic findings. The treatment of benign struma ovarii is surgical resection only. The cases of malignant struma ovarii may need adjuvant treatment, but recurrence is uncommon.