A 50-year-old man visited a physician due to continued right hypochondrium pain for a period of about two months. He was diagnosed with cholecystitis and was referred to our hospital. On arrival, he presented with mild tenderness in the right upper quadrant. Abdominal computed tomography (CT) showed small gallstones and a thickened gallbladder wall. At the same time, a low-density area expanding from the gallbladder bed was revealed. Magnetic resonance cholangiopancreatography (MRCP) showed a smooth stricture of the common hepatic duct. We suspected chronic cholecystitis and inflammatory change in the liver because of cholecystitis. However, malignant diseases could not be excluded, and conservative treatment with antibiotics was therefore performed. On post-hospitalization day 26, cholecystectomy was performed. Rapid diagnosis of a surgical wedged biopsy specimen of the liver showed infiltration of the hepatic sinusoids by atypical lymphocytes. Malignant lymphoma was highly suspected. After further examination, we obtained the diagnosis of primary hepatic CD5+diffuse large B-cell lymphoma. Cyclophosphamide+doxorubicin+vincristine+prednisolone(CHOP) with rituximab therapy was performed. Complete remission was achieved after 8 courses of therapy. However, tumor recurrence in the floor of the mouth occurred one year after the operation. Salvage chemotherapy is now being performed.