Fatal transfusion-transmitted Babesia microti is rare. Because it is not uniformly reported, its incidence can only be estimated at less than 1:1,000,000 per red blood cell (RBC)-containing product. Transfusion transmission usually occurs in northeastern United States with more than 50 cases now reported.1 The disease is usually asymptomatic; however, in asplenic, elderly, or immunosuppressed individuals, it may be fatal.2 This fatal case is unique because it was contracted in Indiana from an Indiana donor. A 61-year-old woman with end-stage renal disease and congestive heart failure received 4 RBC units for lower gastrointestinal bleeding. Subsequently, she complained of nausea and fever to 39.4°C. Approximately 15 percent of her RBCs contained trophozoites, which were reduced to 1 to 2 percent by RBC exchange. Her treatment included intravenous quinidine and clindamycin and then converted to quinine. Unfortunately, disseminated intravascular coagulation and septic shock developed, and she expired within 1 week. No autopsy was performed. One of the transfused units showed evidence of B. microti infestation by immunofluorescence antibody, immunoglobulin M 1:20, and immunoglobulin G of more than 1:256. Her only risk factor was transfusion, and B. microti was confirmed by the Centers for Disease Control and Prevention morphologically, serologically, and by polymerase chain reaction. The implicated asymptomatic donor recalled exposure to wooded areas but not a tick bite and was permanently deferred. The photomicrograph illustrates polyparasitism with tetrad or Maltese cross formation and polymorphism, all characteristic of Babesia infection.