The French standard chemotherapy for osteosarcoma combines high-dose methotrexate (HDM) and etoposide-ifosfamide (EI) in children and adolescents, and API-AI (doxorubicin-cisplatin-ifosfamide) in adults. We herein present the results of M-EI and API-AI in 18- to 25-year-old patients. Patients, 18-25 years old, received either M-EI or API-AI regimens. M-EI comprised seven M and two EI doses preoperatively then M-EI in standard-risk patients (good histological response without metastasis) and five M-AP (methotrexate-doxorubicin-cisplatin) in high-risk patients (poor histological response, metastasis, and/or unresectable primary), postoperatively. API-AI comprised three API and two AI doses preoperatively, then two AI and two PI in standard-risk patients and five EI in high-risk patients, postoperatively. We analyzed 95 patients 18-25 years of age: 55 received M-EI and 40 API-AI. The groups had similar baseline characteristics. Eighty-nine patients (94%) had surgery. Twenty-nine of 55 M-EI patients (60%) and 16/40 API-AI patients (41%) had good histological responses to preoperative chemotherapy. At 5 years, event-free survival was 50% (95% confidence interval [CI]: 39-60) and overall survival was 65% (95% CI: 54-74). Acute toxicity was similar, without treatment-related deaths. Survival outcomes with M-EI and API-AI were not significantly different. Tolerance was acceptable with both regimens. HDM is thus feasible for young adults. However, our study limitations preclude any definitive conclusions.