We report a woman with acute myeloid leukaemia (AML) type M2 according to FAB classification, showing a t(15;17) apparently identical to that of acute promyelocytic leukaemia (APL) on conventional cytogenetic analysis. Fluorescence in situ hybridization (FISH) using cosmidic probes specific for RAR alpha and PML regions did not show a fusion signal as in APL. The breakpoints were assigned to 15q24.3 and 17q21.1. Detailed molecular analyses did not reveal any involvement of RAR alpha and PML genes. The patient was resistant to several front-line AML treatments and to all-trans retinoic acid (ATRA). These findings reinforce FISH and RT-PCR as useful tools for the characterization of a t(15;17) as the translocation specifically associated with APL.