Acute promyelocytic leukemia (APL) is characterized by a t(15;17)(q22;q21) rearrangement. Additional chromosomal rearrangements have been reported in 25-40% of APL patients. The most common abnormality involving chromosome 17 is ider(17). Here we report the case of a patient with APL with isochromosome 17q combined with ider(17), confirmed by fluorescence in situ hybridization. Cytogenetic data strongly suggest that the involvement of chromosomes 15 and 17 in translocation occurs after formation of the isochromosome 17. The case reported here presents the novel finding of two separate clonal events apparently occurring at the same time in an APL patient.