Sixty patients with chronic myeloid leukemia (CML) underwent bone marrow trephine biopsy at presentation. All the biopsies were decalcified, paraffin-embedded and stained with H&E, Gomori's reticulin and Masson Trichrome. A detailed study of the histology including the morphology and topographic distribution of megakaryocytes was done. 55 patients presented in chronic phase. Of these there were 37 cases (67%) of CML-granulocytic (CML-G) type and 18 cases (33%) of CML-granulocytic megakaryocytic (CML -GM) type. Five cases presented in blast crisis. 73% of CML-G had low-grade fibrosis while 83% of CML-GM had high-grade fibrosis. This was statistically significant. On follow-up 25% of CML-G went into blast crisis while all the CML-GM patients remained stable to date. Bone marrow biopsy is a useful investigation in patients of CML at diagnosis as it provides prognostic information. Evaluation of megakaryopoiesis, grading of fibrosis and localization of blasts are possible on a trephine biopsy.