Pancreatic neuroendocrine neoplasms include well-differentiated pancreatic neuroendocrine tumors (PanNETs) and neuroendocrine carcinomas (NECs) with well-differentiated PanNETs accounting for most cases. Other pancreatic primaries and metastatic carcinomas from other sites can mimic pancreatic neuroendocrine neoplasms. Immunohistochemical studies can be used to aid in the differential diagnosis. However, no specific markers are available to differentiate PanNETs from NETs of other sites. Although NECs are uniformly deadly, PanNETs have variable prognosis. Morphology alone cannot predict the tumor behavior. Although some pathologic features are associated with an aggressive course, Ki67 is the only prognostic molecular marker routinely used in clinical practice.