Pancreatic endocrine tumors (PET's) can be divided on a clinical and pathologic basis into ten classes [insulinomas, gastrinomas (Zollinger-Ellison syndrome), VIPomas (Verner-Morrison syndrome, WDHA, pancreatic cholera), glucagonomas, somatostatinomas, ACTH-releasing tumors (ACTHomas), growth hormone-releasing factor secreting tumors (GRFomas), nonfunctioning or pancreatic polypeptide secreting tumors (non-functioning PET), PET's causing carcinoid syndrome and PET's causing hypercalcemia)]. Recent reports suggest calcitonin-secreting PET's also rarely occur but whether they cause a distinct clinical syndrome is unclear. PET's resemble carcinoid tumors histologically; in their ability to synthesize and frequently secrete multiple peptides such as neuroendocrine cell markers (chromogranins); their biologic behavior and their tumor growth patterns. Both groups of tumors are highly vascular, have high densities of somatostatin receptors and similar tumor localization studies including somatostatin receptor scintigraphy are used for both. PET's, similar to carcinoids causing the carcinoid syndrome, require two separate treatment options be considered: treatment directed against the hormone-excess state and treatment directed against the tumor per se because of their malignant nature. In the last few years there have been advances in tumor diagnosis, localization methods, treatment approaches particularly related to the use of synthetic somatostatin analogues, and the definition of the role of surgical procedures in these diseases. Important other advances include insights into the long-term natural history of PET's particularly from studies of gastrinomas, which allow prognostic factors to be identified and the timing of treatment options to better planned, as well as insights into the molecular basis of these disorders. The latter includes both a description of the molecular basis of the genetic inherited syndromes associated with PET's or carcinoid tumors, as well as an increased understanding of the molecular basis for sporadic PET's or carcinoid tumors. Each of these areas will be briefly highlighted in this presentation.