We report four cases of gastric argyrophil carcinoidosis arising in the oxyntic mucosa of patients with Zollinger-Ellison syndrome as part of type 1 multiple endocrine neoplasia (MEN) syndrome. Multiple mucosal and submucosal carcinoids were seen in combination with innumerable hyperplastic and dysplastic growths of argyrophil endocrine cells disseminated in the entire acidopeptic mucosa. Histochemical and ultrastructural investigation indicated that the argyrophil enterochromaffin-like (ECL) cell, a type of endocrine cell normally restricted to the oxyntic mucosa and very sensitive to gastrin stimulation, was a major component of the carcinoidosis. Five similar cases were found in the literature. Because argyrophil ECL cell carcinoid or carcinoidosis is unusual in patients who have the Zollinger-Ellison syndrome but do not have MEN, we believe that the genetic trait of the MEN syndrome has an important permissive role in the promotion of gastric carcinoids through the hypergastrinemia inherent to Zollinger-Ellison syndrome.