A 68-year-old woman presented with rapidly growing multiple lymphadenopathy, night fever, weight loss, and drenching sweat. Physical examination revealed enlarged liver and spleen. Blood tests revealed pancytopenia, elevated levels of lactate dehydrogenase, and positive results in direct Coombs' test. Computed tomography showed multiple enlarged lymph nodes and hepatosplenomegaly. She was diagnosed with diffuse large B-cell lymphoma after excisional biopsy of the inguinal lymph node. Extensive hypermetabolism of the bone marrow was observed on pretherapy 18F-FDG PET (Fig. A), and this finding was in concordance with the results from bilateral trephine biopsies showing diffuse infiltration of lymphoma cells (Fig. B). Cerebrospinal fluid involvement was ruled out by lumbar puncture. Aggressive hydration with alkalinization of urine was performed to prevent tumor lysis syndrome. Complete remission was achieved after 4 cycles of 3-week combination immunochemotherapy, including cyclophosphamide, doxorubicin, vincristine, prednisolone, and rituximab (Fig. C). Follow-up trephine biopsy of bone marrow and direct Coombs' test also yielded normal results after chemotherapy.