We present two patients with human immunodeficiency virus-1 (HIV-1) infection in whom T-cell non-Hodgkin lymphoma developed, based on pathologic diagnosis, immunophenotyping, and T-cell receptor gene rearrangement. Both cases were positive for human immunodeficiency virus-1 by enzyme-linked immunosorbent assay and immunoblot methods. Histologic sections from each patient showed a high-grade pleomorphic T-cell non-Hodgkin lymphoma, and immunophenotyping demonstrated a prevalence of reactivity for CD4 (helper) over CD8 (suppressor) antigens. T-cell receptor beta-chain gene rearrangement studies revealed a rearranged pattern with either the HindIII or BamHI enzymes, whereas immunoglobulin heavy chain genes retained a germ-line configuration. Viral sequences specific for human T-cell leukemia virus-I, human T-cell leukemia virus-II, or HIV-1 were not detected. Thus, although rare, T-cell non-Hodgkin lymphoma may be observed in HIV-1-infected individuals.