Adequate blood components support is essential in the management of ABO mismatched allogeneic hematopoietic progenitor cell transplant (HPCT) patients.We performed a retrospective analysis of 71 HLA matched related donor (MRD 81.69%) and matched unrelated donor (MUD 18.31%) allogeneic HPCTs at Montefiore Medical Center from 2004 to 2012.Transplants included HPC, Apheresis (87.32%) and HPC, Marrow (12.68%) both as first (64.79%) and second transplant (5.21%) after relapse, with an average CD34+ cell dose transplanted of 6.9 +/-3.42 x l0^6/Kg.Overall mortality (61%) and early mortality not related to relapse at less than 100 post transplant days (PTD) (30%) was evaluated.ABO and other red blood cell (RBC) antigen mismatches were evaluated as risk factors for delayed engraftment.Mismatches were defined by direction of incompatibility as Major (11.27%), Minor (16.90%) or Bidirectional (8.45%).Engraftment expressed as average PTD +/-SD, for Absolute Neutrophil Count (ANC 12.9 +/-3.9), Platelets (PLT 17.9 +/-15.17) and RBC was evaluated statistically using univariate analysis.We also used ABO type conversion for mismatched transplants (122.30+/-87.3, range 10 to 334 PTD) and transfusion support as surrogate markers of delayed erythroid and PLT engraftment.ABO mismatched HPCT required significantly higher amount of red cell transfusion (8.2 vs.4.7 Units per 100 days p=0.004).This was true for both major and minor incompatible transplants, and was independent of age, sex, diagnosis, donor type, transplant type, number of transplants and CD34 dose.We also analyzed benefits and risks of transfusion to prioritize transfusion decisions.Management of pre and post-transplant transfusions and apheresis support will be reviewed.