Forty children with relapsed or refractory Acute Lymphoblastic Leukemia (ALL) or Acute Myeloid Leukemia (AML) entered the study and received the association of clofarabine (40 mg/m2/day) in combination with etoposide (100 mg/m2/day) and Cyclophosphamide (440 mg/m2/day) in 1 or 2 induction cycles End point were complete remission (CR)or CR without platelet recovery (CRp) and toxicity