Purpose To examine the clinical presentation, treatment and results in children and adolescents with primary mediastinal (PM) and retroperitoneal (RP) germ cell tumors (GCTs). Methods The TGM95 trial for malignant GCTs was conducted in France between 1995 and 2005 to evaluate a strategy adapted to prognostic factors with cisplatin‐based chemotherapy and surgical management. We reviewed patients with TGCTs at PM and RP sites. Results Among 239 patients, there were 16 patients with PM and 5 with RP tumors, which represent 9% of all patients, highlighting the rarity of these extragonadal locations. A bimodal demographic distribution was observed (11/21 patients <5 years old and 7/21 patients >12 years old). A majority of patients presented with bulky tumors that required urgent care with neoadjuvant chemotherapy. In all patients, elevation of alpha‐fetoprotein indicated a yolk sac tumor component. Human chorionic gonadotrophin was elevated in five patients (four adolescents), suggesting a choriocarcinoma or seminoma component. The diagnosis was based on elevation of these tumor markers in addition to imaging. Chemosensitivity was observed for a majority of patients. An aggressive surgical approach allowed a microscopic complete resection in 12/15 patients with PM tumors and 4/5 with RP tumors. Overall, 14/16 and 4/5 patients survived, respectively. Three adolescents died of tumor progression. Conclusion In children with mediastinal or RP GCTs, the prognosis is favorable when a strategy of delayed aggressive surgery is performed after cisplatin‐based chemotherapy. Younger patients have a better prognosis. Relapses were observed only in adolescents and could not be cured.