Rhesus alloimmunization has become a rare clinical entity, at least in industrialized nations. It is more than 80 years since neonatal hydrops, anemia, and jaundice were first recognized as a single disease characterized by perinatal hepatosplenomegaly, extramedullary hematopoiesis, and nucleated red blood cells (RBCs) on the peripheral smear. What followed is a fetal success story. Levine and coworkers identified a decade later that the rhesus (Rh) antibodies on the RBCs of affected but not unaffected neonates were the cause of the anemia. The basic “story” was 60% completed 7 years later when Chown proved that transplacental fetal-to-maternal hemorrhage was a cause of maternal isoimmunization. In 1961, hemolytic anemia became the first treatable fetal disease after Liley characterized its natural history and then successfully transfused affected fetuses intraperitoneally with adult RBCs. Freda and colleagues completed the basic story when they demonstrated in 1964 that passive immunization of Rh-negative individuals with Rh-positive antibodies prior to purposeful exposure to Rh-positive RBCs prevented immunization.