In Japan, ABO-incompatible kidney transplantation has been performed in more than 1000 patients since 1989, and recently accounts for about 18% of all living donor kidney transplants. As for outcomes, since 2001 the 1-year and 3-year graft survival rates have increased to 96% and 94%, respectively, which are similar to those in ABO-compatible transplantation. These improved outcomes are attributed to a clearer understanding of the mechanisms underlying accommodation and acute antibody-mediated rejection, permitting the development of new therapeutic strategies. This review classifies and discusses the clinical significance of acute antibody-mediated rejection due to ABO-blood-group-related antigens during the critical period preceding the establishment of accommodation.