We describe a case of incidental detection of anti Kell antibody in a child with transfusion dependent thalassaemia. Kell antibody detection may be missed by routine indirect antiglobulin test (IAT) crossmatch procedure because of low prevalence of Kell antigen in the general population. A false negative result can be avoided by using sensitive cross matching techniques and screening cells representing antigens in homozygous state, against all clinically significant antibodies. A transfusion alert card describing the nature of antibody and future transfusion policy should be given to such allo-immunized patients.