A VIPoma or vipoma () is a rare endocrine tumor that overproduces vasoactive intestinal peptide (thus VIP + -oma). The incidence is about 1 per 10,000,000 per year. VIPomas usually (about 90%) originate from the non-β islet cells of the pancreas. They are sometimes associated with multiple endocrine neoplasia type 1. Roughly 50–75% of VIPomas are malignant, but even when they are benign, they are problematic because they tend to cause a specific syndrome: the massive amounts of VIP cause a syndrome of profound and chronic watery diarrhea and resultant dehydration, hypokalemia, achlorhydria, acidosis, flushing and hypotension (from vasodilation), hypercalcemia, and hyperglycemia. This syndrome is called Verner–Morrison syndrome (VMS), WDHA syndrome (from watery diarrhea–hypokalemia–achlorhydria), or pancreatic cholera syndrome (PCS). The eponym reflects the physicians who first described the syndrome.