Duodenal neuroendocrine tumors (NETs) are rare tumors, consisting of five different types of tumors. In many cases, they may be asymptomatic, leading to delay in diagnosis. Clinical symptoms are related to local tumor growth and mucosal ulceration. We report a 38-year old man with duodenal gangliocytic paraganglioma causing overt upper gastrointestinal bleeding and anemia. We describe specific clinical and histopathological features of the tumor, and review the diagnostic and therapeutic strategy. Gangliocytic paragangliomas are regarded as benign tumors. However, the disease recurrence and the malignant potential of the tumor have also been reported.