X-ray contrast examination of the upper gastrointestinal tract in a 73-year-old man with nocturnal heartburn demonstrated a constant filling defect in the duodenum. Gastroduodenoscopy revealed a 4 x 3 cm polypoid mucosal change of the duodenal wall adjacent to the pancreas. Histological examination of an endoscopically obtained biopsy showed a tubulovillous adenoma with severe mucosal dysplasia. The affected segment of duodenum was resected. Serial sections showed extensive focal carcinomatous degeneration of an adenoma. The postoperative course was unremarkable. At endoscopy 30 months later, when the patient was free of any symptoms, there was no macroscopic or microscopic evidence of recurrence. Experience so far indicates that villous adenoma of the duodenum should be treated by radical surgery.