A 70-year-old woman presented with acute fever, impaired consciousness, leukopenia, thrombocytopenia, and right inguinal lymphadenopathy. A lymph node biopsy was diagnosed as diffuse large B-cell lymphoma (DLBCL). However, her symptoms were consistent with severe fever with thrombocytopenia syndrome (SFTS), and RT-PCR for SFTS virus (SFTSV) RNA was positive. The patient’s condition and lymphadenopathy gradually improved with supportive measures and short-term steroid treatment and no lymphadenopathy recurrence was observed. Lymph node pathological examination revealed SFTSV-infected cells, leading to the final diagnosis of necrotizing lymphadenitis associated with SFTS. Careful consideration is required to differentiate necrotizing lymphadenitis associated with SFTS from that associated with DLBCL.