Sixty-three children and adolescents with benign and malignant ovarian tumors were seen at Children's Hospital of Los Angeles in a 21-year period (1961 through 1981). Fifty-four of them received their initial surgery at Children's Hospital; the remaining nine were treated elsewhere and referred to that institution. Clinical records of the 63 patients were reviewed by the present authors. The patients ranged in age from 15 months to 17 years. Abdominal pain was the most common complaint. The duration of pain varied from 12 hours to 3 years. Of the 54 patients first seen at Children's Hospital, 22 presented with torsion of the tumors and Fallopian tubes. All of these patients had histories of nausea or vomiting, and some had fever. In 21 of the 32 patients without torsion, the median duration of pain was about 2 months; the remaining 11 had no pain at all. Abdominal enlargement was noted in 10 of the 54 patients. Constipation, diarrhea, urinary symptoms, vaginal bleeding, and weight gain were other presenting symptoms. On physical examination, the most common sign was a palpable abdominal mass (in 45 of the 54 patients seen first). In each of two patients, an abdominal mass was detected during administration of anesthesia for cystos-copy. Lower abdominal tenderness, fullness, and abdominal distention were noted in several girls, and two presented with precocious puberty. Among the 54 patients seen first, abdominal x-ray films showed calcification in 24 (all with benign teratomas). A mass without calcification was found in each of 16 patients, 9 of them with teratomas and 7 with other tumors. Nine had urinary tract obstruction secondary to pressure from the tumor. The nine patients referred to Children's Hospital after surgery elsewhere had malignant tumors, and two had liver or lung metastases on admission. In 50 of the 54 patients seen first, ovarian tumor was the preoperative diagnosis. In the other four, the preoperative diagnosis was acute appendicitis. Fifty-six patients were diagnosed as having germ cell tumors and seven of these had epithelial tumors. Of the 56 germ cell tumors, 47 were classified as teratomas, 6 as germinomas (2 bilateral), 1 as endodermal sinus tumor, and 2 as mixed germ cell tumors. In the teratoma group, 41 were considered benign (2 bilateral), 3 were teratomas with embryonic components, and 4 were malignant teratomas. The median size of the teratomas was 10 cm, but one benign teratoma in a 14-year-old patient was 37 cm in diameter. In the epithelial tumor category, one was diagnosed as a cystadenocarcinoma and six as cystodenomas (two bilateral). One girl with a cystadenoma had mosaic Turner's syndrome, and another had dysplasia of both ovaries. The sizes of the cystadenomas varied from 4 to 30 cm in diameter. Of the 47 patients with benign tumors (41 teratomas, 6 cystadenomas), it was possible to excise the tumors and preserve the ovaries in 6. Sixteen patients underwent oophorectomy, 24 (61 per cent) had salpingo-oophorectomy, and 1 patient with bilateral tumors had a bilateral oophorectomy plus a unilateral salptngectomy. Thirty-seven patients have remained well for 1 month to 11 years after diagnosis. Ten were lost to follow-up. Of the 13 patients with malignant tumors, 2 underwent unilateral oophorectomy, 2 had bilateral oophorectomy, 6 underwent unilateral salpingo-oophorectomy (all with partial or total omentectomy, and 1 with partial cystectomy), and 1 had bilateral salpingo-oophorectomy and hysterectomy for bilateral germinomas. Two other patients presented with widespread metastases and had biopsies of their tumors as the primary procedures. One of these patients, however, improved with chemotherapy and underwent unilateral salpingo-oophorectomy and hysterectomy 6 months later. The malignant tumors were classified and the patients were staged retrospectively according to the International Federation of Gynecologists and Obstetricians (FIGO) system. Among the three patients with malignant teratomas, an 8-year-old girl with stage IA tumor (germinoma and embryonal carcinoma) had unilateral salpingo-oophorectomy and omentectomy but no additional therapy. She is well 17 years after dagnosis. Another patient, 81/2 years old, with stage IIIB (embryonal carcinoma and choriocarcinoma), underwent unilateral oophorectomy, omentectomy, and partial cystectomy and received postoperative radiation and chemotherapy for 2 years. She has remained well while receiving hormonal substitution therapy for 12 years since the operation. A third patient had a unilateral salpingo-oophorectorny elsewhere for a stage IIIB malignant teratoma (embryonal carcinoma and choriocarcinoma) but did not receive additional therapy. Widespread disease was noted at reexploration 31/2 months later. The patient died 12 days after the second operation.