AbstractWe report a case of chronic myeloid leukemia with spontaneous splenic rupture as the initial presenting feature; there was a successful surgical outcome, but this case terminated in megakaryoblastic transformation. Results are reported based on morphological, immunological, cytochemical, ultrastructural, immunocytochemical studies, and in vitro liquid culture studies. The megakaryocytic nature of the blast cells was identified through the demonstration of platelet peroxidase activity by ultrastructural cytochemistry and the presence of platelet and megakaryocyte‐specific antigen using monoclonal antibody, as well as the anti‐factor VIII antibody by immunocy‐tochemical tech