Chronic Myeloid leukemia is a clonal disease of multipotent haematopoietic cells associated with specific cytogenetic changes involving a translocation t(9;22) (q34:q11), more commonly known as Philadelphia Chromosome (Ph1). A total of 525 patients with CML (480 adults and 45 children) diagnosed at the Nizam's Institute of Medical Sciences, Hyderabad, formed the subjects of this study. Hematological investigations were carried out using standard methods. Unstimulated peripheral blood samples and/or bone marrow aspirates were used for cytogenetic analysis. Hematological evaluation at presentation showed that 435 were in chronic phase, 36 in accelerated phase and 54 in blast crisis. Chromosomal analysis revealed that 86.3% were Ph1 positive and 13.7% Ph1 negative. Additional chromosome changes observed during blast crisis included an extra Ph1 chromosome, Trisomy 8 and Trisomy 19. The results were correlated with survival pattern and prognosis of patients following certain treatment protocols.