Primary pancreatic lymphoma (PPL) is extremely rare, comprising fewer than 1% of non-Hodgkin lymphomas. The most common histological subtype of PPL is diffuse large Bcell lymphoma (DLBCL). A 46-year-old man presented with indigestion, epigastric pain, and weight loss for 2 months. Abdominal computed tomography showed a well-defined hypodense mass located at the pancreas head involving the stomach, as well as enlargement of several mesenteric and perigastric lymph nodes. Histological examination was performed by upper gastrointestinal endoscopy of the stomach and endoscopic ultrasound-guided fine-needle aspiration and biopsy of the pancreatic mass. Histology of the pancreatic mass and the stomach revealed pancreatic DLBCL, involving the stomach. The patient received chemotherapy and is currently in complete remission. We report a rare presentation of DLBCL, appearing as a primary pancreatic tumor involving the stomach, which we presume is the first such report in South Korea.