Primary pancreatic lymphoma (PPL) is an extremely rare form of extranodal malignant lymphoma. The most common histological subtype of PPL is diffuse large B-cell lymphoma (DLBCL). Clinical and imaging features of PPL may often overlap with pancreatic adenocarcinoma. Therefore, it is very important to obtain a preoperative cytohistology diagnosis of pancreatic tumors to avoid unnecessary surgeries in cases with a diagnosis of PPL. Herein, we report a 71-year-old male who was admitted to our hospital with a diagnosis of acute pancreatitis after he presented with complaints of nausea, vomiting, and epigastric abdominal pain. MRI of the abdomen revealed a pancreatic head mass, and histopathology and immunohistochemical assessment of the pancreatic lesion established the diagnosis of DLBCL. The patient achieved remission after six cycles of rituximab-cyclophosphamide, doxorubicin (hydroxydaunomycin), vincristine (oncovin), prednisolone (R-CHOP) chemotherapy.