We report the toxicity of high-dose chemotherapy (HDC) based on etoposide, thiotepa and CY (ETC) in children with poor-prognosis Ewing's sarcoma family tumors (ESFTs). A total of 26 patients with high-risk ESFT (metastasis or axis localization or tumor volume >200 ml or necrosis <95%) were reviewed. The conditioning was based on etoposide (600 mg/m(2)), thiotepa (750 mg/m(2)) and CY (120 mg/kg) followed by autologous BM or PBSC rescue. The conditioning regimen was well tolerated, without any toxic deaths. The median time from transplant to a neutrophil count of >0.5 x 10(9)/l was 10 days (range 6-27) and 22.5 days (range 9-114) for a plt count of >50 x 10(9)/l. Oral mucositis was recorded in 20 patients, grade 1/2 in 19 and grade 3 in the last patient. Diarrhea grade 1/2 was recorded in four patients and grade 1/2 liver toxicity in four patients. Sepsis was documented in four cases and skin toxicity in three. Lung and tubular toxicity, respectively, were reported in one patient each. We conclude that the ETC regimen presented a limited and manageable toxicity. Further studies would confirm the role of ETC in high-risk ESFT.