Objective of the study is to research the epidemiological aspects of maternal alloimmunization against erythrocyte antigens of fetuses (AB0, Rhesus, Lewis, Kell, Duffy and others) and to identify the most common types of hemolytic disease of the newborn (HDN) in the West Herzegovina region. Study Design The 20-year retrospective epidemiological study includes all pregnant women who had been immunologically tested and newborn treated for HDN. Results The indirect antiglobulin (IAT) detected antibodies against antigens in 545 (1.8%) pregnant women of the 29 663 who were tested at the Department of Transfusion Medicine. During the 20-year-long study 310 (1.0%) newborn with HDN were treated. Our results indicate that 42% (230/545) of the pregnant women had AB0 immunization. The most common form of HDN is AB0 HDN 64% (199/310), whereas RhD HDN was treated in 19% (59/310) of the newborn infants. ETR was performed on 29 (19%) infants, 21 (72.4%) with AB0 HDN, and 7 (26%) with RhD HDN. Conclusion This 20-year-long study concludes that, even though there has been significant progress in the prevention of immunization and proactive treatment of HDN, precautionary measures are still required as is the need for gynecologists and obstetricians to be active. The reasons for this are the non-existence of preventive measures for non-RhD immunization, the irregular immunological screening of RhD positive women in pregnancy in the region encompassed by the study in the past few years. The above raises new questions and recommends further research and monitoring of immunization and HDN treatment worldwide.