The 8p11 myeloproliferative syndrome (EMS) is a rare hematologic malignancy characterized by myeloid hyperplasia, eosinophilia, and precursor lymphoblastic lymphoma, associated with balanced translocations involving chromosome 8p11, most commonly t(8;13)(p11;q12). Approximately 75% of EMS patients present with or develop precursor T-cell lymphoblastic lymphoma, and most subsequently develop acute myeloid leukemia. Here we describe the morphologic and immunophenotypic features of 6 cases of t(8;13)-positive bilineal lymphoma of mixed T-cell and myeloid lineage, 5 in lymph nodes and 1 in breast. The patients, 3 males and 3 females, ranged in age from 6 to 19 years. Histologically, each tumor was composed of 2 distinct cellular components: small to medium-sized T cells with scant cytoplasm that resembled lymphoblasts, and larger immature-appearing cells with more abundant eosinophilic cytoplasm that resembled myeloblasts, a subset of which expressed myeloid antigens. In all cases, the latter component tended to surround residual lymphoid follicles and/or blood vessels. Numerous eosinophils and prominent high endothelial venules were present in all of the lymph node specimens. Interestingly, cells of both components expressed CD3 on immunohistochemical stains. In conclusion, EMS associated with t(8;13) should be suspected in patients with a bilineal tumor that involves lymph nodes or other extramedullary sites. We believe that these bilineal neoplasms of mixed T-cell and myeloid lineages, which present as lymphoma, are analogous to bilineal leukemias. They likely arise from an early hematopoietic cell with potential to differentiate along T-cell and myeloid pathways.