A survey of pathogenesis, pathobiochemistry, pathological anatomy, clinic, diagnostics and therapy of the Zollinger-Ellison-syndrome is given. The Zollinger-Ellison-syndrome is, it is true, relatively rare, but its limitation from the usual peptic ulcer has great practical consequences. The suspicion of a Zollinger-Ellison-syndrome is aroused by therapy-resistent ulcers, which in every third person are associated with a diarrhoea, by recidivations of ulcer after gastric operations and by a large basal secretion of acid. The decisive diagnostic means is the serum gastrin determination. The only promising therapy is, as a rule, the gastrectomy.