OBJECTIVES: Peripheral Blood Transplant (PBT) accounted for three-quarters of the Hematopoietic Cell Transplant (HCT) from unrelated donors in the past decade, which indicates it has largely replaced Bone Marrow Transplant (BMT) as the preferred graft source. This shift occurred due to evidence suggesting faster neutrophil and platelet engraftment with the former. However, clinical evidence favoring PBT for other outcomes is inconclusive. Although meta-analyses have compared outcomes for PBT and BMT from related donors, no such analysis has been conducted for unrelated donor procedures. Our objective is to conduct a meta-analysis comparing the outcomes in patients undergoing allogeneic unrelated donor HCT comparing PBTvs.BMT METHODS: We conducted a systematic literature search(PUBMED,CANCERLIT and Cochrane databases) identifying randomized trials and retrospective studies comparing outcomes of allogeneic unrelated donor PBTvs.BMT. We extracted longitudinal transplant outcomes, including acute graft-versus-host disease(GVHD) grade II to IV(aGVHD), chronic GVHD(cGVHD), overall-survival(OS), transplant-related mortality(TRM), disease-free survival(DFS) and relapse from published Kaplan-Meier curves. We used the inverse variance method(Cochrane RevMan5.3.5) to estimate pooled hazard ratios(HRs) and 95% confidence-intervals(CI). HR value<1.00 for an outcome signified PBT as the favorable option compared to BMT. RESULTS: One randomized trial and five retrospective studies were included in the analysis. PBT was significantly less favorable than BMT on aGVHD [HR(1.30),CI(1.15 to 1.47)] and cGVHD [HR(1.32), CI(1.16 to 1.49)]. We didnot find statistically significant differences in other outcomes:OS [HR(1.02),CI(0.86 to 1.21)], DFS [HR(1.00),CI(0.91 to 1.10)], Relapse [HR(1.02,CI (0.78 to 1.34)] and TRM [HR(0.98),CI(0.77 to 1.24)]. CONCLUSIONS: Although PBT is the predominant mode of allogeneic HCT, our meta-analysis found no outcomes for which PBT is favorable compared to BMT.  The only statistically significant comparisons indicated increased hazard of acute and chronic GVHD with PBT. While PBT may offer other clinical advantages over BMT that merit weight in clinical decision-making, its failure to demonstrate significant improvements in overall survival, disease-free survival and transplant-related mortality and increased risk of GVHD calls current clinical practice into question.