Composite lymphoma (CL) is defined as the occurrence of two distinct types of lymphoma within the same patient. Most cases of CL involve Hodgkin and non-Hodgkin lymphomas or two distinct types of B-cell lymphomas; true CL is a composite B-cell and T-cell lymphoma, and is rare. We herein report a case involving concurrent extranodal NK/T-cell lymphoma, nasal-type and diffuse large B-cell lymphoma, which has not been previously reported. As the mechanisms and treatments of composite B-cell and T-cell lymphomas are unclear, further studies are required to improve the prognosis.