The case of a 49-year-old man with peripheral T-cell lymphoma arising in Behcet disease (BD) is reported. A diagnosis of incomplete BD was made, and the patient was treated with immunosuppressive agents for 9 months. A left perirenal mass emerged, and a computed tomography-guided needle biopsy of the tumor revealed the infiltration of small- and medium-sized lymphoma cells. The cells were positive for CD3, CD8, CD45RO, CD43, granzyme B, and T-cell intracellular antigen-1. A diagnosis of non-Hodgkin's lymphoma (diffuse medium, T-cell) was made. A left orbital mass also appeared. Standard combination chemotherapy diminished the perirenal and orbital lesions. Lymphoma cell infiltration in the esophagus was detected after chemotherapy, and the patient died of massive bleeding from the gastrointestinal tract. Non-Hodgkin's lymphoma is rarely associated with BD, and only 7 cases have been reported in the literature. We have summarized the published case reports of malignant lymphoma arising in BD. To our knowledge, this case report is the first to describe cytotoxic T-cell lymphoma arising in Behçet disease.