ABSTRACT. The aim of this study was to evaluate myeloid expression in acute lymphoblastic leukemia (ALL) in children and adolescents who had been referred to the Oncology Department in a hospital in the State of Maranhão based on demographic, laboratory, and clinical data. Myeloid expression was evaluated in 65 patients under 18 years of age who were diagnosed with morphological, cytochemical, and immunophenotypes of ALL. Demographic, laboratory (hemogram), and clinical variables were obtained from medical records. The sample was divided into groups with and without anomalous myeloid expression to analyze the variables. Myeloid expression was observed in 49.2% of the sample. Platelet count was significantly lower in the group of children without aberrant myeloid expression (33,627 platelets/mm 88.9% of children with B-cell ALL without myeloid expression showed less than 50,000 platelets/mm 3 (P = 0.01). Thus, platelet count may be an important parameter in the diagnosis of children with ALL without myeloid aberrant expression and may indicate a greater risk of bleeding during treatment in this group.