Lymphocyte predominance Hodgkin's disease (LPHD) is a B-cell lymphoproliferative disorder; patients with LPHD have an increased risk of developing synchronous or metachronous B-cell non-Hodgkin's lymphoma. The synchronous presence of LPHD and B-cell lymphoma in the same lymph node in some cases lends support to the argument that the B-cell lymphoma arises as a consequence of transformation or progression of LPHD. We have recently identified three cases of LPHD occurring simultaneously with T-cell lymphoma in a series of 76 cases of LPHD in the files of the Nebraska Lymphoma Study Group Registry. In large areas of the lymph nodes, atypical T cells with large, irregular, and hyperchromatic nuclei were admixed with Reed-Sternberg variants characteristic of LPHD (L&H cells). However, in all cases, areas of typical nodular LPHD without obvious T-cell lymphoma were also evident. In one case, frozen-section immunohistochemistry demonstrated the absence of expression of CD5, CD4, or CD8 by the T-cell lymphoma. The L&H cells in all cases expressed CD45 and CD20, as expected. In all three cases, clonal T-cell receptor (TCR)-gamma gene and TCR-beta gene rearrangements were documented by polymerase chain reaction analysis and Southern blotting, respectively. No clonally rearranged immunoglobulin genes were detected by either technique. To our knowledge, this represents the first report of the simultaneous occurrence of LPHD and T-cell lymphoma. Although B-cell lymphoma occurring in the setting of LPHD is a well-recognized phenomenon, previous reports of T-cell lymphoma occurring after a diagnosis of LPHD, as well as our cases with synchronous disease, suggest that the association of T-cell lymphoma and LPHD may not be uncommon as well. Furthermore, our cases indicate that T-cell lymphoma occurring in LPHD is not therapy related. However, the underlying mechanisms by which these composite lymphomas occur remain unknown.