We report the case of a 33-year-old man who presented with a large B-cell non Hodgkin's lymphoma presenting as acute pancreatitis. Abdominal CT showed diffuse swelling of the pancreas, with two distinct masses in the corpus and the tail. Thoracic CT showed a markedly enlarged mediastinum, with a voluminous mass in the middle mediastinum. Direct biopsy of this mass revealed a large B-cell lymphoma. Chemotherapy followed by peripheral blood cell autotransplantation led to complete disappearance of the pancreatic and mediastinal masses. Fatty diarrhea occurred after chemotherapy, probably owing to gland destruction by lymphomatous infiltration. Twenty-six months later, the patient is disease-free but continues to require pancreatic enzyme supplements.