Splenic marginal zone lymphoma (SMZL) is a rare malignant B-cell neoplasm, usually with an indolent clinical course and favorable prognosis. Treatment options include chemotherapy, surgery, radiation and immunotherapy. In some recent studies an increased incidence of hepatitis C virus (HCV) infection in patients with SMZL was reported and its possible role in lymphomagenesis was emphasized. A 66-year-old woman with twelve-year history of HCV infection was admitted due to locally advanced abdominal tumor involving the spleen and the left part of the diaphragm. Transaminase serum levels were not elevated. Neither peripheral lymphadenopathy nor bone marrow pathology was found. Absolute blood lymphocyte, erythrocyte and platelet counts were normal. A splenectomy with partial diaphragm resection in one block was performed. Recovery was uneventful. Pathologic examination with immunohistochemistry revealed SMZL and confirmed a neoplastic infiltration of the resected diaphragm. Following surgery, chemotherapy (CHOP regimen) and immunotherapy (anti-CD20 antibody) were given. At the last follow-up 15 months after surgery, the patient was free of any symptoms of lymphoma. Surgical resection of even locally advanced SMZL with involvement of adjacent tissues can be performed as a diagnostic and therapeutic procedure. Splenectomy is especially indicated in symptomatic patients without other sites of the disease. HCV infection may result in increased risk of SMZL due to the induction of B-cell lymphoproliferation. Because of possible lymphoma regression following anti-viral therapy, a systematic screening for HCV in patients with SMZL seems to be valuable and helpful for treatment planning.