ider(9)(q10)t(9;22)(q34;q11.2) is an isochromosome for the long arm of a derivative chromosome 9 generated by a t(9;22), resulting from the deletion of the short arm of chromosome 9. It is known to be rarely observed in acute lymphoblastic leukemia (ALL) or lymphoblastic crisis transformed from chronic myelogenous leukemia. We herein describe a 26-year-old female patient with precursor B-cell ALL, cytogenetically characterized by ider(9)(q10)t(9;22). Fluorescence in situ hybridization analysis showed two ABL-BCR fusion signals on the derivative chromosome 9 and one BCR-ABL fusion signal on the derivative chromosome 22. Although a t(9;22) and a deletion of the short arm of chromosome 9 are known to be associated with a poor prognostic factor in acute lymphoblastic leukemia, a larger study is needed to determine the prognosis of ider(9)(q10)t(9;22) cases.