We describe a patient who underwent successful BMT from her sibling for the treatment of adult T-cell leukemia/lymphoma. Pre-transplant examination of the donor revealed oligoclonal integration of HTLV-I proviruses within the germ line, and our concern was that clinical sequelae of HLTV-I infection might become evident in the setting of post-transplant immunosuppression. However, the patient has been in complete remission for 14 months after transplantation, and no clonality of HTLV-I provirus was detected in the peripheral blood cells using southern blotting analysis. Our experience supports the possibility of transplantation from HTLV-I positive donors.