Lymphoblastic lymphomas are usually B- or T-cell neoplasms. There exists a small group of T-cell lymphomas additionally coexpressing cytotoxic or natural killer (NK)-cell markers, supporting the hypothesis of a common T/NK-cell precursor and respective neoplasms. Clinically, lymphatic neoplasms of T/NK-cell phenotype are either extranodal lymphomas or acute leukemias. The clinical course of these T/NK neoplasms cannot be predicted by morphology and/or phenotype alone. However, the expression of a heterogeneous (T + NK or myeloid) marker profile or of "early" antigens (such as TdT, CD10, RAG1, RAG2) render them more likely to be in the acute leukemia group. We present a case of a 63-year-old woman with a bone marrow infiltrate, enlarged lymph nodes, and B-symptoms. A cervical lymph node biopsy showed a monomorphic blastic infiltrate with a T-cell phenotype, coexpressing NK markers (CD56, CD57, NK1) and B-cell antigens (CD20, CD79). To the best of our knowledge, this is a newly recognized phenotype that has not been reported before. T/NK-cell lymphomas, including blastic NK-cell leukemia/lymphoma and T-lymphoblastic lymphomas, have to be included in the differential diagnosis. Both groups have a different clinical behavior and prognosis. In particular, T/NK-cell lymphomas associated with an Epstein Barr virus infection are clinically very aggressive neoplasms.