The authors report a case of a 58-year-old man with bilateral proptosis and signs of orbital inflammation without any associated systemic findings. MRI showed diffuse orbital infiltration. An intraconal orbital biopsy revealed polyclonal lymphoplasmacytic infiltration and non-necrotizing lymphoid small-vessel vasculopathy. The orbital symptoms resolved following a 2-week course of oral prednisone. Three months later, the patient experienced abdominal pain and weight loss. Ultrasonographic investigation showed hepatosplenomegaly, a retroperitoneal mass, and inguinal lymphadenopathy. A lymph node biopsy revealed a diffuse large B-cell lymphoma. The patient underwent chemotherapy but died 6 months later with metastatic disease. This case suggests that diffuse orbital inflammation with nonspecific vasculitis may be an early paraneoplastic finding associated with diffuse large B-cell lymphoma.