The aim of this study was to identify risk factors associated with PFS in patients with Ewing sarcoma undergoing ASCT; 116 patients underwent ASCT in 1989-2000 and reported to the Center for International Blood and Marrow Transplant Research. Eighty patients (69%) received ASCT as first-line therapy and 36 (31%), for recurrent disease. Risk factors affecting ASCT were analyzed with use of the Cox regression method. Metastatic disease at diagnosis, recurrence prior to ASCT and performance score <90 were associated with higher rates of disease recurrence/progression. Five-year probabilities of PFS in patients with localized and metastatic disease at diagnosis who received ASCT as first-line therapy were 49% (95% CI 30-69) and 34% (95% CI 22-47) respectively. The 5-year probability of PFS in patients with localized disease at diagnosis, and received ASCT after recurrence was 14% (95% CI 3-30). PFS rates after ASCT are comparable to published rates in patients with similar disease characteristics treated with conventional chemotherapy, surgery and irradiation suggesting a limited role for ASCT in these patients. Therefore, ASCT if considered should be for high-risk patients in the setting of carefully controlled clinical trials.