Chromosomal abnormalities play an important role in genesis of Acute Lymphoblastic Leukemia and have prognostic implications. This work is aimed at detecting common chromosomal translocation and associated fusion oncogenes in adult ALL patients and their relationship with clinical features and treatment outcome by using RT-PCR and interphase FISH. Five most common fusion oncogenes i.e. BCR-ABL, ETV6-RUNX1, MLL-AF4, SIL-TAL1 and TCF3-PBX1, were found in 79 percent of the patients in the sample. BCR-ABL and MLL-AF4 characterized a subset of adult ALL patients with aggressive clinical behavior and a poor outcome. Survival in ETV6-RUNX1 was better while SIL-TAL1 had frequent organomegaly and usually showed up with a platelets count less than 50x109/l. TCF3-PBX1 fusion oncogene was associated with lymphadenopathy. This is the first comprehensive study from Pakistan which investigates the frequency of fusion oncogenes, their association with clinical features, treatment response and outcome. This information will help in the prognostic stratification and risk adapted management of adult ALL patients in under developed countries like Pakistan.