Adenomatous polyposis (AP) diseases, including familial adenomatous polyposis (FAP), attenuated FAP (AFAP), and MUTYH-associated polyposis (MAP), are the second most common hereditary causes of colorectal cancer. A frequent extracolonic manifestation of AP disease is duodenal polyposis, which may lead to duodenal cancer in up to 18% of AP patients. Endoscopic surveillance is recommended at 0.5-to 5-year intervals depending on the extent of polyp growth and histological progression. Although the Spigelman classification is traditionally used to determine surveillance intervals, it lacks information on the (peri-) ampullary site, where 50% of duodenal carcinomas are located. Hence, information on the papilla has recently been added as a prognostic marker. Patients with duodenal adenoma(s) ≥10 mm and ampullary adenomas of any size are suggested to be referred to an expert center for endoscopic therapy, particularly endoscopic mucosal resection and endoscopic ampullectomy. Nonetheless, despite the logic of this approach, the long-term efficacy of endoscopic therapy is still to be demonstrated.