Familial adenomatous polyposis (FAP) is an autosomal dominant disease characterized by the development of multiple colonic polyps and an almost 100% lifetime risk of colon cancer.1, 2, 3 With an incidence of 1 case per 10 000 people and caused by a mutation in the APC gene,3, 4, 5 FAP may be associated with extraintestinal manifestations—usually benign—but in up to 1.2% of cases, it can be linked to well-differentiated nonmedullary thyroid carcinoma of the classic and cribriform-morular papillary subtypes, as first described in 1968 and 1999, respectively.5 This evidence concerns the gene APC and Familial adenomatous polyposis.