Hemolytic disease of the newborn secondary to rhesus alloimmunization was once a major contributor to perinatal morbidity and mortality. Today, rhesus immune globulin has markedly decreased the prevalence of this disease so that only one to six cases occur in every 1000 live births. The rarity of this condition warrants consideration of consultation or referral to a maternal-fetal medicine specialist. Once sensitization occurs, rhesus immune globulin is no longer effective. Evaluation for the presence of maternal anti-D antibody should be undertaken at the first prenatal visit. First-time sensitized pregnancies are followed with serial maternal titers and, when necessary, serial amniocenteses to detect fetal bilirubin by DeltaOD(450). In cases of a heterozygous paternal genotype, new deoxyribonucleic acid techniques now make it possible to diagnose the fetal blood type through amniocentesis or even from plasma/serum deoxyribonucleic acid analysis. When there is a history of an affected fetus or infant, maternal titers are no longer diagnostic as a screening test. Serial peak middle cerebral artery velocities using Doppler ultrasound can be used in these pregnancies to detect fetal anemia. In some situations, intrauterine transfusion is necessary through ultrasound-directed puncture of the umbilical cord with the direct intravascular injection of red cells. Perinatal survival rates of more than 90% have been reported; hydrops fetalis reduces the chance for a viable outcome by up to 25%. Immediate neonatal outcome is complicated by the need for repeated transfusions secondary to suppressed erythropoiesis. Long-term studies have revealed normal neurologic outcomes in more than 90% of cases. Future therapy will involve selective modulation of the maternal immune system making the need for intrauterine transfusions a rarity.