The potential role of the infused B cell subset after Hematopoietic Stem Cell Transplantation has not been yet studied. The present study analyzed the impact of B cells on transplant outcome in 254 patients who received a bone marrow graft from a human leucocyte antigen-identical sibling donor. The influence of B lineage-specific hematopoietic progenitor cells (CD34(+) CD19(+)) and B cells (immature and mature B cells, CD34(-) CD19(+)) was also analyzed. All included patients received a myeloablative regimen. The cumulative incidence function of acute graft-versus-host (GvHD) grade II to IV was 48% and was inversely associated with the number of CD34(+) CD19(+). There were no statistically significant associations between B cell subsets and chronic GvHD or survival. The CD34(+) CD19(+) B cell subset remained significantly associated with acute GvHD in multivariate analysis (Relative risk = 0.32, 95% confidence interval: 0.11-0.92, P = 0.035). In conclusion, a higher B lineage-specific hematopoietic progenitor cells (CD34(+) CD19(+)) cell dose is associated with a significant decrease incidence of acute GvHD.