Background: Immunophenotypic characterization of acute leukemia is an important clinicalrnapplication of flow cytometery and has become a powerful tool contributing to proper diagnosisrnand classification.rnObjective: To phenotype and classify acute leukemias by flow cytometry using commonly usedrnmarkers for leukemia diagnosis.rnMethod: A total of 40 pediatric and adult patients diagnosed with acute leukemia were evaluatedrnby flow cytometry with 17 surface and cytoplasmic markers known to be useful in discriminatingrndifferent types of acute leukemia.rnResults: 21 of 40 patients (52.5%) were classified as Acute Myeloblastic leukemia (AML) whilern19 (47.5%) were identified as Acute lymphoblastic leukemia (ALL). Of all the ALL cases, 10 ofrnthe 19 (52.6%) were B-ALL and 47.4% (9/19) were T-ALL. Markers of immaturity HLA-DRrnand CD34 antigens were co expressed in 61% of AML cases, and 33% of T-ALL cases, whereasrnCD34 was expressed in 50% of the B-ALL cases. MPO and CD13 were the most commonlyrnexpressed markers of AML, whereas CD19 and cCD79a were present in all cases of B-ALL.rnCytoplasmic CD3 and CD7 were the most sensitive markers for T-ALL. Discrimination of AMLrnfrom ALL patients by flow cytometry was 80% concordant with traditional morphology. Notablerndiscrepancies occurred in cases where leukemia cells expressed markers for more than onernlineage.rnConclusion: Immunophenotyping by flow cytometry provides useful information to confirmrndiagnoses of standard morphology methodology, to provide classifications where morphology isrnindeterminate, and to provide further lineage and maturation information for ALL not obtainablernby morphology is needed for ALL cases. It thus represents an important tool among many inrnleukemia classification and is realistic in the resource limited settings.rnKey words: Leukemia, ALL, AML, Flow cytometry, Immunophenotyping