A case of a young female patient affected by Zollinger-Ellison syndrome with occult gastrinoma during exploratory laparotomy, is reported. On the basis of transhepatic portal catheterization the patient underwent pylorus preserving pancreatoduodenectomy according to Longmire-Traverso. A malignant gastrinoma of the duodenal wall, 2 mm in diameter, was observed on the operative specimen in the suspected gastrinogenic area. The procedure led to complete clinical recovery of the patient who did not respond to the medical treatment of the ulcer. The prognosis was good with oncologic radicality of surgery confirmed at follow-up and excellent digestive function.