Primary pancreatic lymphoma (PPL) is an extremely rare malignant tumor that accounts for less than 2% of extranodal malignant lymphomas and 0.5% of pancreatic tumors. The most common symptoms of PPL are abdominal pain (83%), abdominal mass (58%), and weight loss (50%). The final diagnosis of PPL is based on cell histology, and the most common histological subtype is diffuse large B-cell lymphoma (DLBCL). The number of reported cases of primary pancreatic mucosa-associated lymphoid tissue (MALT) lymphoma is limited. The conversion rate of MALT lymphoma varies between 3% and 12%. However, the transformation of primary pancreatic MALT lymphoma to DLBCL has not been reported. We present a case of a 58-year-old man whose main symptoms were nausea and vomiting. Magnetic resonance imaging of the abdomen showed space-occupying lesions in the neck and body of the pancreas. Histopathological examination after surgical resection was diagnosed as primary pancreatic MALT lymphoma. Local radiotherapy was recommended and rejected by the patient's family. The disease progressed in a short time. Left supraclavicular lymph node resection biopsy and pathological examination showed DLBCL. After the initiation of chemotherapy, glaucoma appeared in the right eye during treatment, and chemotherapy was suspended. The disease progressed rapidly and the patient eventually died.