OBJECTIVE: To study the prognostic factors for events-free survival (EFS) in children with acute non-mature B-lymphoblastic leukemia.METHODS: One hundred and sixty-one children with newly diagnosed acute non-mature B-lymphoblastic leukemia received the ALL-XH-99 protocol treatment. Their medical data, including clinical, biological and molecule features, early responses to treatment (bone marrow evaluation on the 19th day of induction therapy), minimal residual disease (MRD) in bone marrow after remission induction therapy, the risk grade of disease before the beginning of chemotherapy and the outcome, were retrospectively studied.RESULTS: Univariable analysis indicated that the gender and P170 levels before therapy had no effect on the outcome. Age, initial white blood cell count (WBC), prednisone response, early response to treatment, fusion genes (BCR/ABL or MLL/AF4) and MRD level were significantly related to the EFS (P<0.01). Immunophenotype, myeloid-associated antigen and the risk grade of disease were also related to the EFS (P<0.05). Multivariable analysis showed that WBC ≥50×109/L, Cμ positive, BCR/ABL or MLL/AF4 positive and MRD positive (≥0.01%) were risk factors for the poor prognosis (P<0.01). The early response to treatment was important to modify the therapy protocol. CONCLUSIONS: WBC ≥50×109/L, Cμ positive, BCR/ABL or MLL/AF4 positive and MRD positive have important prognostic values in childhood acute non-mature B-lymphoblastic leukemia. Early response to treatment is an important index for modifying the chemotherapy protocol.