After excluding the typical causes, the underlying etiology of severe acute pancreatitis is often elusive; tumors are on the differential but may be difficult to prove in the absence of a discrete mass on imaging. In this report, we describe the case of an elderly woman with diffuse large B-cell lymphoma masquerading as acute pancreatitis. To our knowledge, only twelve other cases of pancreatic B-cell lymphoma presenting as acute pancreatitis have been described. However, while other cases involved well-circumscribed tumors of the pancreas, this is the first known case of pancreatic lymphoma of a diffusely infiltrating pattern presenting as acute pancreatitis.