Immune hemolysis is one of the adverse effects that can occur following hematopoietic cell or solid organ transplantation. Understanding the clinical settings and the various causes of immune hemolysis is necessary for prompt diagnosis and appropriate management. One of the important causes is the passenger lymphocyte syndrome, which occurs following minor ABO blood group incompatibility between donor and recipient. Hemolysis in this syndrome is often modest in severity but may be severe and even life-threatening. Major ABO blood group incompatibility is also associated with hemolysis, although this is relatively unusual and generally not severe. Autoimmune hemolytic anemia is a relatively common late complication of allogeneic transplantation and carries significant risk of mortality. Also, alloantibodies may be produced by engrafted cells of the donor's immune system or by residual cells of the patient's immune system following hematopoietic cell transplantation. Hemolysis may occur after solid organ transplantation, particularly as part of the passenger lymphocyte syndrome.