Objectives Non‐functioning gastrin‐producing neuroendocrine neoplasms (NEN) of the duodenum are rare gastrointestinal tumors without a clinical syndrome due to gastrin production. Their incidence has significantly increased as an incidental finding during endoscopic studies. The aim of this study was to describe the characteristics and prognostic factors of this emergent and infrequent neoplasm. Methods We performed a retrospective observational study based on the duodenal NENs samples with positive staining for gastrin at the Department of Pathology, University Hospital 12‐de‐Octubre (Madrid, Spain) between 2000 and 2017. Patients with clinically functional tumors ([Zollinger–Ellison syndrome] or gastrin >1000 pg/mL), with previously diagnosed multiple endocrine neoplasia (MEN) syndrome or synchronous neoplasia were excluded. Clinicopathological and therapeutic variables, follow‐up, recurrence, and mortality data were collected. Results In all, 21 patients were included. Most of the tumors were diagnosed incidentally as a single small polypoid lesion limited to mucosa/submucosa and with a low histological grade. Four (19.0%) patients presented with metastatic involvement at diagnosis (lymphatic and/or hepatic). These four patients also had a high or intermediate mitotic grade and infiltration further than submucosa. Local resection was applied in most cases as curative treatment. There were two cases of tumor recurrence and two tumor‐related deaths with a 5‐year disease‐free survival of 81.0%. Conclusions The majority of these tumors were diagnosed at a localized stage and had a good prognosis with treatment. Nevertheless, given the potential metastatic risk, a close follow‐up is necessary, especially in those with aggressive pathological factors such as deep infiltration or high histological grade.