A duodenal polyp was found during a health check of a 71-year-old asymptomatic man. Duodenoscopy demonstrated a pedunculated, smooth-surfaced tumor of 18 mm in size, protruding from the minor papilla. Endoscopic ultrasonography demonstrated a homogeneously low-echoic submucosal tumor. Enhanced computed tomography and magnetic resonance imaging demonstrated a well-enhanced duodenal tumor without obvious metastasis. A tumor biopsy revealed a well-differentiated neuroendocrine tumor, and laparotomic transduodenal polypectomy with regional lymph node dissection was performed. The histology of the surgical specimen revealed gangliocytic paraganglioma consisting of three cell types: endocrine, ganglion, and spindle cells. There has been no recurrence in >5 years after surgery.