Hematopoietic stem cell transplantation (HSCT) can either cause or eliminate autoimmune disease. Here, we report two cases. One was a 33-year-old woman with myelodysplastic syndrome (refractory anemia) who received bone marrow transplantation from her human leukocyte antigen (HLA)-identical sister who had a history of Graves disease. Antithyroid antibodies, including antimicrosomal antibody and antithyroglobulin antibody, appeared 4 months after transplantation. Clinical hyperthyroidism appeared 7 months after transplantation, and a hypothyroid state was noted 2 months later. The other case was a 50-year-old woman with Sjgrens syndrome and hypothyroidism who was diagnosed with peripheral T cell non-Hodgkins lymphoma. She received allogeneic peripheral blood stem cell transplantation (PBSCT) from her histocompatible sister owing to only partial response to traditional chemotherapy. Cure of lymphoma and remission of Sjgrens syndrome was noted 4 years after PBSCT. These two illustrative cases, one of acquisition of hyperthyroidism and the other of remission of Sjgrens syndrome after transplantation, highlights that HSCT can induce adoptive autoimmune disease or cure coincidental autoimmune disease. Donor selection and attentive monitoring is required in such circumstances.