BACKGROUND: Primary pancreatic lymphoma is a rare but treatable malignancy (less than 1% of pancreatic tumors) that may be clinically confused with pancreatic adenocarcinoma.
METHODS: In a patient with upper abdominal pain, ultrasonography and CT detected a mass in pancreatic head, which compressed the common bile duct. The patient received a Whipple’s operation and intraoperative frozen sections of the mass showed an anaplastic carcinoma. Immunohistochemical staining was used to indicate the origin and prognosis of tumor.  
RESULTS: Grossly the tumor involved the pancreatic head, soft in consistence and invaded part of the gastric wall. Histologically, the tumor was composed mainly of large and moderate neoplastic cells, which were diffusely positive for CD20 and Bcl-6 antigens, indicating the features of diffusely large B cell lymphoma.
CONCLUSIONS: The proper diagnosis of the tumor should be made with CD20 and Bcl-6 immunohistochemical study. Radical surgery is indicated for resectable carcinoma but not for a chemosensitive lymphoma.