We report a case of villous adenocarcinoma of duodenum arising from the ampulla of Vater with a review of the literature. Although preoperative endoscopic biopsies were performed, no malignancy was identified. Because of the pathological uncertainty we decided to perform a pylorus-preserving pancreatoduodenectomy. Microscopic examination demonstrated glandular dysplasia with aspects of villous adenoma and well differentiated adenocarcinoma. We conclude that both in malignant cases and in cases with uncertain diagnosis a pylorus-preserving pancreatoduodenectomy is the best surgical treatment because it results in better 5 year survival.