Based on the hypothesis that long-term fetomaternal microchimerism is associated with acquired immunologic hyporesponsiveness to noninherited maternal antigens (NIMAs) or inherited paternal antigens (IPAs), several groups have recently reported successful cases of non-T-cell-depleted hematopoietic stem cell transplantation (SCT) from HLA-haploidentical family members mismatched for NIMAs. In this study, we examined the outcomes of 35 patients with advanced hematologic malignancies who underwent HLA-2-antigen- or HLA-3-antigen-incompatible SCT from a microchimeric NIMA-mismatched donor. After standard-intensity or reduced-intensity preparative regimens, all patients had sustained hematopoietic recovery with tacrolimus-based graft-versus-host disease (GVHD) prophylaxis. Grade II/IV acute GVHD occurred in 19 (56%) of 34 evaluable patients, while extensive chronic GVHD developed in 13 (57%) of 23 patients who could be evaluated. Multivariate analysis demonstrated that NIMA mismatch in the GVH direction was associated with a lower risk of severe grade III-IV acute GVHD when compared with IPA mismatch (P = .03). Fifteen patients were alive and 14 of them were disease-free with a median follow-up of 20 (range, 8 to 37) months. These results indicate that T cell-replete SCT from an HLA-haploidentical NIMA-mismatched donor can offer durable remission with an acceptable risk of GVHD in selected patients with advanced hematologic malignancies who lack immediate access to a conventional stem cell source.