Significant peripheral eosinophilia in association with acute graft-versus-host disease (GVHD) is rare. Here we report a case of eosinophilia in a 30-year-old woman with relapsed acute myelogenous leukemia after an allogeneic bone marrow transplant who was treated with donor lymphocyte infusion (DLI). A month after the DLI, she developed a pruritic erythematous rash, hepatic enzyme elevations and eosinophilia that peaked at 23,300 cells/mm3. A diagnosis of acute GVHD was made and the patient was treated with corticosteroids with a resolution of all of the aforementioned findings. The authors suggest that eosinophilia in a bone marrow transplantation patient should raise suspicion of GVHD.