The presence of the Philadelphia chromosome (Ph’) has important diagnostic and prognostic implications in a number of Haematological disorders. The abnormality is characteristic of Chronic Myeloid Leukaemia (CML), found in around 90% of cases but represents a significant abnormality in 30% of adult and 2 to 10% of childhood Acute Lymphoblastic Leukaemia (ALL) cases. This rearrangement is also seen in rare cases of acute myelogenous leukemia (AML). As a result of the Philadelphia translocation, t(9;22)(q34;q11), the ABL1 (Abelson) proto-oncogene and the BCR (Breakpoint Cluster Region) gene fuse, giving rise to the BCR/ABL1 hybrid or ‘fusion’ gene. The translocation between chromosomes 9 and 22 can be accompanied by loss of proximal sequence (ASS1/ABL1) and distal 22q found in ALL and rare cases of AML. The deletion of 9q encompassing the ASS1 gene is associated with poor prognosis and the time to disease progression on imatinib treatment is shorter. Therefore the establishment of the atypical patterns in the BCR/ABL1 translocation may have clinical diagnostic and prognostic implications.