Preservation of fertility was carried out in 28 young patients with malignant germ cell tumors of the ovary from 1962 through 1987. The pathologic diagnosis was immature teratoma in 16, endodermal sinus tumor in 7, dysgerminoma in 2, and germ cell tumor of mixed type in 3. At laparotomy, 16 patients were proved to have stage I disease, 1 had stage II disease, 9 had stage III disease, and 2 had stage IV disease. The tumor was confined to one ovary in all 22 cases treated for the first time, and the preserved ovary and uterus were normal in all 6 referred cases with recurrent diseases. Postoperative chemotherapy was given to all patients except two with stage I immature teratoma. Persistent remission was achieved in 22 patients; 5 patients died and 1 was lost to follow-up. The duration of follow-up was more than 1 year for all surviving patients, more than 3 years in 16 cases (72.7%), and more than 5 years in 13 cases (59.1%). The menstrual periods were normal in all except 3 cases, of whom 2 were below the age of 12 and one failed to menstruate at the age of 21 with a hypoplastic uterus and underdeveloped secondary sex characters. Among 12 married patients, 7 of 10 desirous of child-birth became pregnant during follow-up. Of these, 6 had a normal term delivery and 1 is currently pregnant. The preliminary conclusion is that preservation of fertility for young patients with malignant germ cell tumors of the ovary, regardless of the stage of the disease, is a safe and practicable procedure in the absence of involvement of the contralateral ovary and uterus.