Acute promyelocytic leukaemia (APML/AML M3) is characterised by chromosomal rearrangements of 17q21 leading to the formation of fusion proteins involving retinoic acid receptor alpha (RARA). Also a majority of cases are characterised by the presence of the t(15;17)(q22;q12-21) which involves the promyelocytic leukaemia (PML) gene. Two chimeric genes PML-RAR is detected in 100% of AML patients and RAR-PML detected in 40% of AML patients. The detection of the PML-RARA fusion gene by quantitative polymerase chain reaction (RT-PCR) is routinely used for diagnosis and monitoring of minimal residual disease (MRD). The detection of MRD in patients with APML identifies molecular relapse and enables the prediction of haematological relapse.