Background: We compared toxicity and outcomes of BuMel and TreoMel HDCT consolidation with stem cell rescue in high-risk ES pts prospectively treated in 5 consecutive trials at the Istituto Ortopedico Rizzoli, Bologna, Italy. Methods: Eligible pts had histologically proven diagnosis of ES, high-risk disease defined as localized disease with poor histological/radiological response to standard chemotherapy or lung/pleural metastases or extra-pulmonary metastases or relapsed disease, were aged < 40. All pts received previous standard chemotherapy (vincristine, ifosfamide, doxorubicin, etoposide, cyclophosphamide actinomycin-D) and surgery and/or radiation therapy (RT) as local treatment. From June 1, 2011, TreoMel was used instead of BuMel to avoid potential severe complications related to busulfan, as in case of previous RT on axial skeleton/pelvis. Pts with lung metastases received lung irradiation 12-15 Gy at least 2 months after HDCT. Results: Between January 1, 2007, and September 30, 2018, 98 pts received BuMel or TreoMel: 52 pts with localized disease (7 TreoMel), 26 pts with lung/pleural metastases (5 TreoMel), 10 pts with extra-pulmonary metastases (4 TreoMel) and 10 pts with relapsed disease (1 TreoMel). Median age was 18 yrs (range 3-39 yrs). 14 out of 17 TreoMel pts received previous RT on axial skeleton/pelvis. Median follow up is 4.2 yrs (range 10 mo. - 12 yrs). Pts treated with TreoMel showed a significant lower incidence of grade 3-4 stomatitis (p = < 0.001) and of all grade ≥ 3 non-hematological toxicities (p = < 0.001). One pt died of BuMel-related toxicity (sinusoidal obstruction syndrome/veno-occlusive disease) and none after TreoMel. For localized ES, the 5yr-EFS was 66.7% (95%CI, 47.9-78) for BuMel pts and 66.7% (95CI%, 19.5-90.4) for TreoMel pts. Conclusions: In high-risk ES, TreoMel is significantly less toxic then BuMel. Combining RT on central/axial sites and TreoMel is feasible. In localized ES, results show similar 5yr-EFS between BuMel and TreoMel. TreoMel could be used instead of BuMel when busulfan is contraindicated.