A papillary (villous) adenoma of the duodenum was found in a 67-year-old male. Radiographic barium studies of the upper gastrointestinal tract revealed a tumor in the second portion of the duodenum. Biopsied specimens taken through a duodenofiberscope showed papillary adenoma. A partial duodenectomy with duodenojejunostomy was performed. The specimen was a pedunculated tumor measuring 3 X 2 X 1.5 cm. Histologically, the tumor was composed of villous and tubular arrangements of mucus-secreting columnar epithelial cells. A moderate number of entero-endocrine cells and a few Paneth cells were also noted. Forty-two other cases reported in Japan are briefly reviewed.