BACKGROUND Molecular cytogenetics is becoming one of the most useful tools targeting some genes which are generally considered to lead to leukemic transformation (as well as for numerical abnormalities). A fraction of acute lymphoblastic leukemia (ALL) cases carry the translocation t(9;22) (q34;q11.2) which juxtaposes the ABL proto-oncogene to the BCR gene generating a chimeric gene, BCR/ABL. This aberration is more frequent in adult ALL (20%-40%) than in pediatric ALL (<5%), and predicts poor clinical outcome. AIM OF OUR WORK: Is to study BCR/ABL fusion gene in ALL cases using fluorescent in situ hybridization. METHODS Twenty newly diagnosed ALL patients, 16 adult and 4 paediatric cases, were included in the study, 11 cases (55%) were of precursor B phenotype, 8 cases (40%) belonged to T lineage, while one case was biphenotypic expressing mainly precursor B cell markers tether with CD13, CD33, CD117, Detection of BCR/ABL fusion gene was done using interphase FISH technique and was confirmed molecularly using the RT-PCR technique. RESULTS BCR/ABL fusion gene was negative in all the examined cases, yet abnormality involving 9q34, ABL gene, either by addition or deletion was detected in three cases (15%). Two of these cases were associated with BCR gene extra copies (three and four copies, respectively). CONCLUSIONS This may reflect the frequency of association of ABL gene and BCR gene abnormality in our cases, and that absence of fusion gene BCR/ABL does not exclude their role in the leukomogenic process, yet a larger study is required to confirm and detect the prevalence of these gene disturbances in ALL and their association.