Many gastric acid hypersecretory states (basal acid output of greater than 15.0 mEq/h) exist for which the etiology is known, such as Zollinger-Ellison syndrome, systemic mastocytosis, antral exclusion, antral predominant Helicobacter pylori gastritis (antral G cell hyperplasia), chronic gastric outlet obstruction, short gut syndrome and basophilic leukemias. However, many hypersecretory patients have no identified etiology for their acid hypersecretion and are designated as idiopathic gastric acid hypersecretors with a basal acid output of greater than 10 mEq/h and a normal serum gastrin level. Because of the gastric acid hypersecretion these patients also commonly have an increased frequency of stools. Idiopathic gastric acid hypersecretion represents a known cause of gastric acid hypersecretion that is far more common than Zollinger-Ellison syndrome and it has a markedly different treatment regimen and natural history. We report a case of a patient with idiopathic gastric acid hypersecretion previously misdiagnosed as having Crohn's disease because of a presenting complaint of diarrhea and mimicking Zollinger-Ellison syndrome because her fasting serum gastrin level was elevated when incorrectly measured in the presence of antisecretory treatment.