We describe an unusual case of with de novo composite diffuse large B-cell lymphoma and enteropathy-type T-cell lymphoma involving the duodenum in a 65-year-old man with celiac disease. A segmental duodenum resection revealed that two neoplastic components had infiltrated the intestinal wall. The coexistence of two malignancies was confirmed by immunohistochemical and molecular biologic analysis, which revealed clonal T-cell receptor and immunoglobulin heavy chain gene rearrangements. Epstein-Barr virus was not detected in the B- and T-cell components. After chemotherapy, the patient experienced two relapses of enteropathy-type T-cell lymphoma only. We review the medical literature on composite B- and T-cell lymphomas and discuss their diagnosis, pathogenesis, prognosis and treatment.