Autoimmune diseases which follow allogeneic BMT from a donor who is a patient or a carrier of an autoimmune condition are considered to be a paradigm of adoptive autoimmunity. Seven cases of autoimmune thyroiditis associated with clinical hyperthyroidism have been published to date. In the case reported here a 35-year-old female patient with AML of the M2 subtype received unmanipulated PBSC from her HLA-identical sister who had therapeutically controlled Graves' disease. Antithyroid antibodies, including thyrotropin receptor (TSHR) antibodies, appeared 1 year after transplant. Clinical hyperthyroidism requiring thyrostatic medication appeared after 2 years. The biological and clinical implications of adoptive, post-transplant autoimmunity are briefly discussed.