Colorectal polyposis is the main feature of familial adenomatous polyposis (FAP), but benign and malignant lesions have also been described in the stomach, duodenum, small bowel, biliary tract and pancreas. There are few reports on FAP patients with duodenal polyps that developed at a younger age and even fewer on cases with dysplastic degeneration. The progression to carcinoma usually presents quite late in the clinical history of FAP patients, typically at least 20 to 25 years after proctocolectomy. This report described the rare case of a patient presenting with duodenal adenomas with dysplastic changes and tumor infiltration as the first sign of FAP, who was treated by pancreaticoduodenectomy followed by proctocolectomy for subsequent dysplastic changes in colonic polyps.