It has been reported that autoimmunity might be sometimes transferred from a donor to a recipient following allogenic bone marrow transplantation (allo-BMT). We report a patient to whom Basedow disease was transferred from the donor through an allo-BMT. A 18-year-old man with acute lymphoblastic leukemia, received the allo-BMT from his HLA-identical sister. Two-years later, he developed symptoms of palpitations and general fatigue. He was diagnosed as having Basedow disease because of hyperthyroidism, and high levels of the anti-thyroid stimulating hormone receptor antibody and antithyroid antibody. When he received the allo-BMT, his donor had neither the clinical symptoms of Basedow disease, nor abnormal findings on examination to determine her eligibility as a the donor. We retrospectively assayed anti-thyroid antibodies from their cryopreserved sera, and found the donor's anti-thyroid antibody was positive, while her serum was negative before transplantation. It was apparent that the donor had subclinical Basedow disease. The patient has remained in complete remission without any signs of chronic graft-versus-host disease (GVHD) up till the time of writing. It is believed that an anti-thyroid tissue reactive B-cell clone was transferred from the donor to the patient and commenced to produce antibodies. It is suggested that thorough investigation of the donor's autoimmunity is needed before allo-BMT. If the recipient develops an autoimmune disease after allo-BMT, we should definitely investigate the donor's autoimmunity.