RESUMEN
Thalassemia is the most prevalent hereditary anemia worldwide and in our country. Lifelong blood transfusion is currently the treatment protocol of this disease, but it has some side effects; one of them is alloimmunization. Alloantibodies produce antigens against RBCs which patients do not have. The antigens are transmitted via chronic blood transfusion gradually. One of these RBC antigens is antigen I, and the antibody against it is IgM class and cold antibody. Cold agglutinins are capable of agglutinating RBCs in low temperature and may result in hemolytic anemia which is known as cold agglutinin disease [CDA]. In Iran, data regarding incidence of CAD are not available, but incidence of CAD in USA is approximately 1:300000. An 18-year-old man with beta-thalassemia major referred to the hematology lab for periodic checking of blood smear. He had clumps of RBC and RBC indices were abnormal. In repeated examination, he was known to be asymptomatic for purpose of cold agglutinins. We do not have any records or information about cold agglutinins in thalassemic patients in Iran. This case was detected only through periodic laboratory tests without any special complications on the part of the patient