Fasting serum gastrin levels greater than 1000 pg/ml are said to establish the diagnosis of gastrinoma in a patient with peptic ulcer disease. The authors observed a patient with recurrent peptic ulcer disease, diarrhea, and a fasting serum gastrin of 1044 pg/ml who had a gastrocolic fistula, not the Zollinger-Ellison syndrome. The provocative tests of gastrin secretion, including secretin infusion and standard meal test, were helpful in ruling out a gastrinoma. This is the first reported association of gastrocolic fistula and hypergastrinemia. The patient demonstrates that the differential diagnosis of markedly elevated serum gastrin should be expanded to include gastrocolic fistula.