Chronic myelogenous leukemia (CML) is characterized by the presence of a Bcr-Abl fusion protein with deregulated tyrosine kinase activity that is required for maintaining the malignant phenotype. Imatinib as a selective inhibitor of Bcr-Abl induces complete cytogenetic remission in the majority of patients with CML in chronic phase. Targeted therapy of CML with imatinib favors the manifestation of Ph-(negative) clone disorders in some patients. Facts indicate that patients on imatinib should be followed with conventional cytogenetics, even after induction of complete remission. We report a case of a patient with CML, in chronic phase treated with imatinib which induces the most common abnormality trisomy 8.