Acute lymphoblastic leukaemia is primarily a children's disease, 75% of cases occur in children under six years of age. B-cell phenotype constitutes 80-85% of ALL. The lymphoblasts in ALL vary from small blasts with scant cytoplasm, condensed nuclear chromatin and indistinct nucleoli to larger cells with moderate amounts of light blue to blue-grey cytoplasm, occasionaly vacuolated and multiple variably prominent nucleoli. The nuclei are round, irregular or convoluted. Coarse azurophilic granules are present in some lymphoblasts. In some cases, lymphoblasts have a cytoplasmic pseudopodia (hand mirror cells). Cytochemistry seldom contributes to the diagnosis of ALL. Lymphoblasts are negative for myeloperox. but they may show PAS positivity, usually in the form of coarse granules and sometimes may react with non-specific esterase with multifocal punctate or Golgi zone pattern. There are no unique morphologic or cytochemical features in lymphoblastic leukaemia with recurrent genetic abnormalities. Acute myeloid leukemia comprises nearly 25% of pediatric leukemias. Myeloblasts vary from small to large cells with moderate to abundant dark blue to blue-grey cytoplasm. The nuclei are round to oval with finely granular chromatin and usually several nucleoli. The cytoplasm may contain azurophil granules. Detection of myeloperoxidase indicates myeloid differentiation but its absence does not exclude a myeloid lineage because early myeloblasts as well as monoblasts may lack myeloperoxidase activity. Promyelocytes are large cells with irregular, kidney-shaped or bilobular nuclei. Cytoplasm is marked by numerous granules and may contain bundles of Auer rods. Myeloperoxidase reaction is strongly positive. Monoblasts are large cells with abundant light grey to deep blue cytoplasm. The nuclei are round or convoluted with delicate, lacy chromatin and one or more large prominent nucleoli. They are usually strong positive for non-specific esterase with no or week myeloperoxidase activity. Promonocytes have a delicately convolutes or grooved nucleus and finely granulated cytoplasm. Most promonocytes express myeloperoxidase and non-specific esterase activity.Megakaryoblasts are medium to large size with round or irregular nucleus with one to three nucleoli and basophilic agranular cytoplasm, sometimes with cytoplasmic blebs or pseudopods.They are myeloperoxidase negative.