Sinus histiocytosis with massive lymphadenopathy (SHML) is a distinct benign clinicopathological entity, characterized by painless enlargement of lymph nodes due to sinus histiocytosis. Here, we report a case of SHML with diffuse large B-cell lymphoma. A 64-year-old man was admitted to our hospital because of fever. He presented with enlargement of a small cervical lymph node and huge abdominal paraaortic lymphadenopathy. Cervical lymph node biopsy revealed SHML and bone marrow biopsy showed infiltration of large B-cell lymphoma. Several cases of SHML associated with lymphoma have been documented to date, but this type of simultaneous occurrence has not yet been reported.