We report a case of adult T-cell leukemia (ATL) with complex chromosome abnormalities including an inversion (10)(q11q24) in a 64-year-old man. Although some abnormalities of chromosome 10 have been seen in ATL and other lymphoid neoplasias, inv(10)(q11q24) has previously been reported only in a case of T-cell chronic lymphocytic leukemia. Recent studies have revealed a rearrangement of a novel homeobox-containing gene called TCL-3 or HOX11 on 10q24 in T-cell acute lymphoblastic leukemia with the specific chromosome translocation t(10;14)(q24;q11), and thus the significance of 10q24 aberrations in leukemogenesis is indicated. We suggest that, despite the rarity of this anomaly, inv(10) (q11q24) may be a new chromosome inversion related to T-cell neoplasia and that the 10q24 anomaly may be an important cytogenetic clue for the elucidation of the pathogenesis of some peripheral T-cell neoplasias.