Chromosome translocation t(15;17), the breakpoints of which are in the PML gene on chromosome 15 and retinoic acid receptor-alpha (RAR alpha) gene on chromosome 17, is specifically found in acute promyelocytic leukemia (APL). Clinically typical APL without t(15;17) and with the PML-RAR alpha fusion transcripts or rearrangements in PML and/or RAR alpha gene has been reported, suggesting submicroscopic changes at the molecular level without apparent t(15;17) or observation of normal metaphases. Trisomy 8 is common in APL as a secondary chromosomal abnormality in addition to t(15;17), as well as in acute myelogenous leukemia in general, but it is rare as a sole chromosomal anomaly in APL. PML-RAR alpha fusion transcript was detected in an APL case with trisomy 8 but without t(15;17), indicating that the leukemic cells lacked t(15;17) and still expressed the PML-RAR alpha fusion transcripts. This indicates that the same submicroscopic molecular changes as in APL with t(15;17) do occur in APL without t(15;17) and supports the use of molecular analysis for PML-RAR alpha fusion in APL.