This report concerns 142 infants and children with teratomas treated from 1960 to 1984. The primary site of tumor was sacrococcygeal in 84, ovarian in 15, testicular in 15, mediastinal in 14, retroperitoneal in 7, cervical in 3, and other in 4. Malignancy occurred in 40 of 142 (28%) patients. Serum for alphafetoprotein (AFP) was obtained preoperatively in 29 patients. Elevated AFP was seen in all patients with malignancy, 3 of 6 with immature lesions and 1 of 19 with a benign lesion. Postoperative rise in AFP levels was a good indicator of malignant recurrence. Beta human chronic gonadotropin (BHCG) levels were only helpful in following teenage boys with testicular lesions. Benign tumors were treated by complete excision alone with a 97% survival. Testicular malignancies had a good prognosis with 13 of 15 surviving (87%) despite distant metastasis in four. In contrast, survival was only 32% with nontesticular malignancies. Survival was 17% for resectable malignant cases treated with surgery alone compared with 100% when operation was followed by multiagent chemotherapy. Unresectable malignant lesions were usually fatal despite multiagent chemotherapy and/or second-look procedures.