A Caucasian woman, with a A+ CCD.ee K neg erythrocyte phenotype and no history of blood transfusion, delivered a first child who developed mild anemia. The direct antiglobulin test performed on the newborn red blood cells belonging to the A+ CCD.ee K neg group, was strongly positive for IgG. During the pregnancy and after the delivery, the woman had a negative irregular antibody screening test, using standard red blood cells. However, at birth, using a collection of thawed red blood cells with rare phenotypes (private antigens), the lab showed an antibody anti-Wr(a) in the maternal serum. The activity of the maternal antibody, with a titer of 16, was completely inhibited by dithiothreitol, indicating the nature IgM of the circulating antibody. The presence of the antigen Wr(a) on the surface of the newborn and its biological father red blood cells was confirmed. The concentration of IgG anti-Wr(a) on baby erythrocytes was demonstrated by the presence of the antibody anti-Wr(a) in the eluate. This case illustrates the difficulties to detect antibodies against private antigens on baby erythrocytes, responsible of hemolytic diseases of newborn. Indeed, standard red blood cell panels used for irregular antibodies screening test do not express generally those private antigens.