A total of 119 children (1990-95) with acute lymphoblastic leukemia (ALL) B-lineage either CD10+ or CD10- were registered into a single non-randomized chemotherapy protocol. Only untreated patients with standard risk were included in the study. Their ages ranged from 1.8-10 years with a mean of 5.1 years. There were 82 (68%) children with early pre B-All, 35 (29%) with pre B-ALL and 2(1.6%) with transitional pre B-ALL (p < 0.00001). The patients were divided according to CD10 reactivity, either + (94 children) or -(25 patients). The event-free survival (EFS) at 60 months for the CD10+ children was of 78% (alive 73/94), while for the CD10- was 71% (alive 18/25) (p = 0.6) and 74% for both groups. The factors that influenced favorably the survival in the CD10+ group were the age between 3 to 5.99 years (p < 0.00001), sex (either male or female), leukocyte count between 10-24.9 x 10(9)/l (p < 0.00001), LDH under 300 U/I (p < 0.00001) and L1 bone marrow cytomorphology (p < 0.00001). In the CD10- patients, the EFS was favorably influenced by the female sex (p = 0.04), leukocyte count under 10 x 10(9)/l (p = 0.05) and LDH < 300 U/l (p = 0.02). CNS infiltration was documented in 4.2% (5/119). Mortality secondary to chemotherapy was seen in 7%. In conclusion, this is the first large series in Mexican children with B-lineage ALL published. Because of the relatively small number of patients in each group (pre B and transitional pre B), all the patients in the current series were treated alike. When the 119 patients were divided only on the basis of CD10 reactivity, the EFS for both groups (CD10+ and-) was similar; therefore, the reactivity to CD10 has no prognostic value in this type of ALL.