Precursor lymphoblastic lymphoma is an uncommon neoplasm. We report the case of a man who presented with precursor T lymphoblastic lymphoma and ultimately received an allogeneic bone marrow transplant from his human leukocyte antigen-identical sister. Four years later he developed recurrent disease. By means of DNA probing for the amelogenin locus and fluorescence in situ hybridization, the neoplastic cells of the recurrent lesion were found to be of donor origin. We offer the report of a patient with an unusual lymphoblastic lymphoma who, after successful bone marrow transplantation, developed the same disease of donor cell origin; further, we offer a literature review on donor cell lymphoma.