Background and Procedure. Outcomes in children with teratomas collected between October 1982 and December 1995 in cooperative protocols of the German Society of Pediatric Oncology and Hematology (GPOH) were analyzed. Teratomas were diagnosed in 329 (42%) of 780 registered patients with germ cell tumors. The annual incidence was 0.24/100,000. Main primary sites were coccygeal (n = 132, 2.2:1 female predominance), ovary (n = 81), testis (n = 40) and brain (n = 15, 2.8:1 male predominance). Results. Two hundred seventy cases of extracranial non-testicular teratoma were evaluated: In mature teratomas (n = 154) the observed relapse rate was 10%. Incomplete resection was the main risk factor for relapse. After complete resection, the relapse-free survival (RFS, Kaplan-Meier-estimation) was 0.96 ± 0.01 (n = 126, observation time 18-155 months) in comparison to an RFS of 0.56 ± 0.09 in incompletely resected teratomas grade 0 (n = 28, observation time 28-94 months) (P < 0.01). Im-mature teratomas were treated by surgery alone in 76 cases and by surgery and adjuvant chemotherapy in 40 cases. The observed relapse risk was 18%. Main risk factors for relapse were incomplete tumor resection (n = 38) as well as immaturity in incompletely resected teratomas. Fifteen of 29 relapsing patients presented with malignant tissue in the recurrent tumor (mainly yolk sac tumor); in contrast, seven of 40 patients with immature teratoma relapsed despite adjuvant chemotherapy without showing malignant components (P = 0.014). Nine of 36 (25%) relapsing patients died of disease. Eleven of the 27 (41%) surviving children suffered from mutilation after repeated surgery. Comments. It is suggested that an international randomized trial for patients with incompletely resected high risk teratoma be initiated to evaluate the effect of adjuvant chemotherapy on specific end-points: 1) influence on relapse rate in general; 2) reduction of the proportion of malignant relapses; 3) avoidance of mutilating surgery.