OBJECTIVE Postengraftment infections are a major cause of transplant-related morbidity and mortality following allogeneic hematopoietic stem cell transplantation (allo-SCT). Allogeneic peripheral blood progenitor cell transplantation (PBPCT) is associated with faster hematopoietic recovery compared to bone marrow transplantation (BMT) and unmanipulated PBPCT may be associated with fewer postengraftment infections. We set out to evaluate and compare the incidence, cause, and outcome of postengraftment infections following HLA-identical sibling T cell-depleted PBPCT vs T cell-depleted BMT between days 30 and 365 posttransplant. METHODS Forty recipients of peripheral blood progenitor cells (PBPC) and 47 recipients of bone marrow (BM) were included. The two groups of patients were comparable with respect to their baseline characteristics. RESULTS PBPC grafts contained significantly more CD34+ cells and PBPCT was associated with significantly faster neutrophil and lymphocyte recovery as compared to BMT. PBPC recipients experienced more chronic graft-vs-host disease (GVHD; 55% vs 34%; p=0.02). The number of definite and clinical infections per 100 patient days was comparable between recipients of PBPC and BM with similar contribution of causative microorganisms. At one year post SCT, 68% of PBPC recipients had experienced at least one CTC grade 3-4 infection vs 65% of BM recipients. Treatment-related mortality at one year from transplantation was 34% after PBPCT vs 30% after BMT, and no difference in infection-related mortality was observed. CONCLUSIONS Postengraftment infectious morbidity and mortality were comparable between recipients of PBPC and BM despite a higher CD34+ cell content of PBPC grafts and faster lymphocyte recovery after PBPCT, which may in part be explained by the higher incidence of chronic GVHD.