B-cell lymphoma, unclassifiable, with features intermediate between diffuse large B-cell lymphoma and classical Hodgkin lymphoma (BCLu-DLBCL/CHL), also known as gray-zone lymphoma, has overlapping clinical and biological characteristics of both diffuse large B-cell lymphoma and classical Hodgkin lymphoma (CHL). These lymphomas are typically associated with mediastinal disease, and extranodal involvement is rare. In the present report, we describe a case of a 78-year-old woman with BCLu-DLBCL/CHL found to have extranodal lesions and no evidence of mediastinal disease. Although biopsy specimens were histologically similar to nodular sclerosis CHL, the tumor cells were positive for CD30 and mature B-cell markers, such as CD20, CD79a, PAX5, BOB.1, and OCT-2, but negative for CD15. Furthermore, the patient had extranodal lesions and an increased level of soluble IL-2 receptor. These findings are unusual in CHL. Therefore, we diagnosed the patient with BCLu-DLBCL/CHL. She received adriamycin, bleomycin, vincristine, and dacarbazine therapy and exhibited partial response. Some cases without mediastinal disease, such as our case, have been reported; however, these cases are rare and further studies are required. © 2013 The Japanese Society for Clinical Molecular Morphology.