A review of the St Mark's Hospital Polyposis Registry has revealed an association between adenomatous polyposis (familial polyposis coli) and thyroid carcinoma. Even though full clinical information was unavailable on all patients in the registry, it is evident that young women (below 35 years of age) are at particular risk of developing thyroid cancer, mainly of a papillary type, their chances of being affected being approximately 160 times that of normal individuals. All patients with adenomatous polyposis should thus have regular thyroid examination.