The reciprocal translocation t(9;22)(q34;q11) which gives rise to the Philadelphia (Ph1) chromosome and BCR/ABL fusion gene, plays a pivotal role in the diagnosis and pathogenesis of chronic myeloid leukemia (CML). In this study, we evaluated the role of fluorescence in situ hybridisation (FISH) in detecting the BCR/ABL rearrangement in CML patients. The sensitivity, specificity and detection rate of BCR/ABL gene using FISH, PCR and conventional cytogenetics (karyotyping) methods were also compared. 18 bone marrow samples of patients with clinically diagnosed CML and suspected of CML were collected. The sensitivity, specificity and positive predictive values of FISH were altogether 100% while the sensitivity, specificity and positive predictive values for conventional cytogenetics (karyotyping) were 85%, 100% and 100% respectively. Convetional cytogenetics (karyotyping) detected an additional chromosomal aberration in addition to the Ph1 chromosome. In conclusion, FISH is a highly sensitive method in detecting the BCR/ABL gene. Conventional cytogenetics (karyotyping) remains an important investigation in the work up of suspected CML patients since there is a possibility of detecting chromosomal aberrations in addition to the Ph1 translocation. Therefore, conventional cytogenetics (karyotyping) and FISH are complementary techniques and their results should be interpreted together with clinical information.