ABO hemolytic disease of the newborn occurs almost exclusively in infants of blood group A and B who are born to group O mothers. Positive Direct Antiglobulin Test (DAT) can identify those infants who are at risk of developing the ABO hemolytic disease. Earlier studies have suggested that BO incompatibility is associated with a positive DAT in black infants. In this study we sought to determine whether ABO incompatibility type could be associated with a higher rate of DAT positivity or clinical hemolytic disease. We reviewed the electronic medical records of all ABO-incompatible births over a 2-year period. There were 1537 ABO-incompatible births during the study period. DAT was more commonly positive among BO incompatible (21.5% in BO vs. 14.8% in AO, P=0.001) and black (18.8% in blacks vs. 10.8% in nonblacks, P=0.003) infants. DAT positivity was significantly associated with both severe hyperbilirubinemia (P=0.028) and hemolytic anemia (P<0.001). BO incompatibility was significantly associated with hemolytic anemia, but not severe hyperbilirubinemia, in the infants tested.