Classification of acute lymphoblastic leukemia (ALL) by flow cytometric immunophenotyping characterizes the disease and delineates potential therapeutic intervention. We retrospectively analyzed CD20 expression in 143 patients with newly diagnosed precursor B-cell ALL. CD20 was observed in 61% of patients at diagnosis. There was no correlation between CD20 expression and age, white blood cell count, or cytogenetic abnormalities. Despite the fact that CD20-positive ALL patients had a tendency toward a worse outcome, there was no significant difference between patients with and without CD20 expression in 3-year overall survival 65 vs. 82% (P = 0.14), and cumulative incidence of relapse 36 vs. 18% (P = 0.3) in pediatric patients and 51 vs. 53% (P = 0.31) and 35 vs. 38% (P = 0.6) in adults, respectively. In conclusion, CD20 expression appears to be more common in Mexican patients with newly diagnosed precursor B-cell ALL higher than in Caucasian populations and lacks prognostic value.