Immunologic phenotype studies were performed on cells and on frozen sections of involved tissue from a 20 year old female with typical T-cell lymphoblastic (convoluted) lymphoma. The cells demonstrated a thymic phenotype but in addition marked with Leu-7 (HNK-1)--an antibody reported to identify human natural killer/killer (NK/K) cells. Normal or neoplastic cells with this phenotype have not been previously reported. These findings support the existence of a thymic precursor for a T-cell subset of Leu-7 + cells. The unusual clinical response to therapy is another feature of this unique case.