B-cell lymphoma, unclassifiable, (BCLU) is a subtype of lymphoma first recognized by the World Health Organization in 2008. Patients with this lymphoma have a very poor prognosis, with a rapidly progressive and refractory clinical course despite intensive therapy. Clinical data remain sparse, and no established therapeutic approach exists for the treatment of BCLU. Although BCLU may currently be under-recognized, its incidence is expected to increase with improved detection. Diagnostic accuracy is critical to prevent under- or overtreatment of patients. Treatments may need to be more intensive and include central nervous system prophylaxis. Development of clinical trials evaluating immunochemotherapy is recommended for this challenging lymphoma subtype. Nurses play a critical role in providing disease and treatment education and assessment, monitoring during therapy, and managing treatment-related side effects. Nurses need to emphasize prevention of chemotherapy complications and timely communication with the oncology healthcare team.