Morphologic and morphometric assessment of megakaryocytes was performed in 15 cases each of chronic myeloid leukemia and idiopathic thrombocytopenic purpura and compared with 15 normal cases. The average size of megakaryocytes was 174.66 μ2 in CML and 407.56μ2 in ITP, which were significantly different than that of normal. There was marked heterogeneity in size and topographic distribution and location of megakaryocytes in CML than in ITP and normal marrow. Megakaryocyte size was also different in differing grades of fibrosis in the marrow. Morphometry of megakaryocytes is a simple tool that may be useful in the diagnosis of disorders affecting megakaryocyte lineage.