A 53-year-old woman with chronic myeloid leukemia received allogeneic hematopoietic stem cell transplantation. After neutrophil engraftment, her platelet count exceeded 100,000/μL at day 64. While she was receiving corticosteroid treatment for chronic graft versus host disease (GVHD), her platelets suddenly dropped to 6,000/μL at day 210 and she was diagnosed with immune thrombocytopenia (ITP). Corticosteroids, intravenous high-dose gamma globulin (IVIg) and a splenectomy failed to increase her platelet count. She developed bacterial pneumonia at day 599 and antibiotic therapy was initiated. Soon after, her platelet count continuously increased. Her GVHD and ITP are now in remission without any ongoing treatment.