Abstract Teratomas in 81 patients seen at the Childrens Hospital of Los Angeles during the years 1941 through June, 1970 were studied. Thirty-six teratomas (44.5 percent) were from the sacrococcygeal area and 30 (37 percent) were ovarian. Teratomas occurred in the testis in 5 patients (6.2 percent), in the retroperitoneum in 4 (5 percent), in the mediastinum in 3 (3.7 percent), and there was one each (1.2 percent) in brain, soft palate, and base of the umbilical cord. In 61 patients, the teratomas contained benign (mature) tissue only. Mature as well as embryonic tissues were found in 10 tumors, and 10 patients had malignant teratomas, with frankly malignant tissue in addition to mature and/or embryonic tissue. Types of malignant component included germinoma (seminoma or dysgerminoma), embryonal carcinoma, yolk sac carcinoma, and choriocarcinoma. Tumors which contained one or more of these malignant elements, but no mature or embryonic tissues, were not included in this series. In patients with teratoma containing frankly malignant tissues, the occurrence of local recurrence and/or metastasis was lethal regardless of therapy. In our series, there has been no survivor among these patients.