We present the case of an adult male patient, where the assessment of cell line could not be done without corroboration of the immunophenotype and cytological analysis. The correct lineage assessment is needed in order to treat the patient correctly. Morphology, cytochemistry, and immunophenotyping were used and the diagnosis we established was B acute lymphoblastic leukemia with aberrant myeloid markers (CD13, CD33). Periodic Schiff Acid stain was very useful to obtain an accurate diagnosis. Adult B acute lymphoblastic leukemia usually has an unfavorable prognosis because of certain cytogenetic abnormalities (Philadelphia chromosome) and different reactivity to treatment. This case strongly supports the continued use of immunophenotyping in the diagnosis and monitoring of acute leukemia and corroboration of different diagnostic techniques for the diagnosis.