Zollinger-Ellison syndrome (ZES) is a typical, intractable, possibly fulminating, peptic ulcer associated with extreme gastric hyperacidity.

In the United States ZES is estimated to occur in 0.1% to 1% of all patients who have duodenal ulcers. Internationally the incidence of ZES varies; for example, Sweden reports 1:1,000,000 to 3:1,000,000; Ireland reports 0.5:1,000,000; and Denmark reports 0.1:1,000,000 to 0.2:1,000,000. ZES has been reported in all races. Males are slightly more likely to be affected than females by a ratio of 1.3:1. The mean age of onset is 43 years.

The majority, about 75%, of ZES cases are the result of a non–β-islet cell, gastrin-secreting pancreatic tumor that stimulates the stomachs acid-secreting cells to their maximum output. The result is profound hyperacidity that can erode gastrointestinal mucosa to the point of ulceration. The remaining ZES cases result from an autosomal dominant familial syndrome, multiple endocrine neoplasia type I (MENI). In MENI, the primary tumor may be found in the duodenum, pancreas, or abdominal lymph nodes but may also be found in so-called ectopic areas, including the heart, ovaries, gallbladder, liver, or kidneys.