Pediatric germ cell tumors (GCTs) are a group of chemosensitive malignancies with a 90% curability rate. We report a series of children with relapsing or therapy-resistant GCT treated with melphalan–etoposide–carboplatin high-dose chemotherapy (HDCT) and autologous stem cell transplantation. This consisted of 18 children, either with GCTs after relapse (nine patients) or with an unsatisfactory response to first-line chemotherapy (nine patients), who underwent HDCT. The HDCT regimens MEC1 (carboplatin 1500 mg/m², etoposide 1800 mg/m², and melphalan 140 mg/m²) and MEC2 (carboplatin 800 mg/m², etoposide 800 mg/m², and melphalan 140 mg/m²) were each used in nine patients. The median observation time was 81 months, the 5-year overall survival (OS) was 76%, and the event-free survival (EFS) was 70.8%. Non-relapse mortality was 0%, and four patients died after HDCT due to progression of the malignancy. No difference in OS or EFS was noted between the MEC1 and MEC2 protocols. The 5-year OS and 5-year EFS were higher in children treated with autologous stem cell transplantation before the age of four years. The presence of metastatic disease or time of HDCT consolidation during first/subsequent line chemotherapy did not affect patient survival. The melphalan–etoposide–carboplatin protocol is feasible in pediatric GCT, but is associated with potentially life-threatening complications. In conclusion, the use of HDCT must be examined in well-designed clinical trials, and the identification of patients who can benefit from this approach is critical to avoid overtreatment.