&NA;A 48‐year‐old man with Gardner's syndrome, who had abdominoperineal resection for rectal carcinoma in 1962, was found to have an ulcerating growth of the duodenum, and pancreaticoduodenectomy was performed in 1979. Histologic examination by complete step‐serial sectioning disclosed a well‐differentiated adenocarcinoma with adenomatous remnants, a large adenoma with focal carcinoma, 256 adenomas of the duodenum, and 91 adenomas of the gastric antrum. The world medical literature was reviewed, and 29 cases of periampullary carcinoma and 12 cases of gastric carcinoma complicating familial polyposis coli or Gardner's syndrome were analyzed.