Cytogenetic studies and Chromosomal analysis of acute lymphoblastic leukemia have helped to identify recurrent chromosomal abnormalities and understanding their effect on leukemogenesis, which proved to have prognostic significance. In the current study, we investigated the presence of chromosome 10 aneuploidy in 12 patients with ALL using FISH technique. Results were compared with flow cytometric derived DNA aneuploidy data in a trial to asses the impact of aneuploidy of chromosome 10 on the clinical, hematological presentation and outcome of therapy. We found that the association of one pair of chromosome 10 with well established bad prognostic markers as high TLC, young age, high peripheral blood blasts, CNS infiltration, higher association with T-ALL immunophenotype and DNA index <1 (hypoploidy) suggest that monosomy ten can be considered as a bad prognostic marker. Also, as a tumor suppressor gene (PTEN) was previously discovered and mapped to chromosome 10, its deletion was proved to be associated with the pathogenesis of different types of tumors. So, we can conclude that deletion of such tumor suppressor gene may be involved in the pathogenesis of ALL among monosomy ALL patients.