This report describes 4 cases of duodenal microgastrinomas associated with a Zollinger-Ellison syndrome. All gastrinomas were solitary tumors located in the submucosal layer of the first (n = 3) or second portion (n = 1) of the duodenum. The tumor size ranged from 0.75 to 8 mm in diameter (mean 4.9 mm). All gastrinomas were classified as malignant with respect to the metastatic spread to regional lymphnodes (n = 4) and liver (n = 1). None of the gastrinomas was identified by the preoperative imaging studies. Three tumors were localized during the surgical exploration, one tumor (0.75 mm in diameter) by the histopathological work-up of the resected specimen. The surgical therapy included two local resections and two Whipple procedures. Except for the patient with hepatic metastases the postoperative serum gastrin was normal indicating complete tumor resection. No patient died because of recurrent or metastastic gastrinoma. In conclusion, microgastrinomas of the duodenum are rarely diagnosed preoperatively because of their small size but can be identified by careful surgical exploration. Considering the high malignancy rate of this tumor patient prognosis depends on radical surgical therapy.