BACKGROUND: The RhD antigen is very immunogenic and is a significant cause of hemolytic disease of the newborn (HDN). The RHD-CE(8-9)-D hybrid allele is commonly associated with a D- phenotype. Here, we report a case of high-titer maternal anti-D and late onset of HDN in a newborn carrying a RHD-CE(9)-D variant supposedly encoding the same partial D antigen as the RHD-CE(8-9)-D allele, but with significant expression of D antigen. STUDY DESIGN AND METHODS: To elucidate the blood group antigen background of the case, we carried out serologic, flow cytometric, and genetics studies of the newborn and his father. CONCLUSION: Individuals carrying the RHD-CE(9)-D allele do express D antigen, but do so at significantly lower levels than those carrying the more common D+ phenotypes (e.g., DCe/dce). It may mitigate and delay otherwise severe HDN in pregnancies complicated by high-titer anti-D.