The distinction between T cells and NK cells is difficult, and becoming more complex, as the diversity of the human lymphocyte repertoire is evident. We report the establishment of a permanent CD8+ NK/T cell line (SRIK-NKL) from a patient with leukemic phase of acute lymphoblastic lymphoma having characteristics of both NK and T cells, and extensively describe its phenotype, including cytotoxic activity, NK cell receptor expression, and other molecules critical for immune function. We further compare SRIK-NKL to other available NK/NK-T cell lines. SRIK-NKL may be useful for studying NK cell development, functions, and modulation, leading to novel strategies for treatment of autoimmune disease, infection, and cancer.