A 15-year-old boy complained of abdominal pain and massive upper gastrointestinal hemorrhage. Endoscopic evaluation demonstrated an ulcerated, submucosal mass involving the ampulla. This was locally excised and found to show the characteristic histologic and ultrastructural features of a gangliocytic paraganglioma. Similar lesions have been reported in 29 patients with a mean age of 55 years (range, 32-80). Twenty-six patients complained of abdominal pain or gastrointestinal bleeding, symptoms that mimic those of peptic ulcer disease. These tumors are uniformly benign, nonencapsulated, and submucosal. They usually arise in the second portion of the duodenum and are treated by simple excision. This patient is the youngest reported, and his case is presented as an illustration of an unusual tumor that can masquerade clinically and radiologically as a duodenal ulcer. The importance of endoscopic evaluation is stressed.