A 52-yr-old man developed immune hemolytic anemia approximately 2 wk after receiving an ABO-minor-mismatch renal transplant. When a Group O organ is transplanted into a non-O recipient or a non-AB organ is transplanted into a Group AB recipient, hemolysis can occur and has been attributed to a form of graft-versus-host disease in which donor plasma cells carried along with the graft produce red blood cell antibodies. In this case, the diagnosis was confirmed when an antibody screen indicated that the organ recipient's serum agglutinated panel red blood cells of the recipient's ABO group. This type of hemolysis usually occurs 1 to 2 wk after transplantation, is limited in duration, and can be severe. If transfusion is required, blood of donor type should be used.