Forty-five polyposis patients with thyroid carcinoma constituted 1.2% of the patients in the Leeds Castle Polyposis Group database. The patients were diagnosed during 1959-1995; 44 were females at a median age of 25 years (range 10-40) and 37 (82%) had papillary carcinoma. At the end of 1995 only one patient (9%) had died from thyroid carcinoma, and the ten-year cumulative survival was 84% (95% confidence limits 72-97). Due to the low incidence of thyroid carcinoma in FAP and the good prognosis we do not recommend a regular thyroid screening in polyposis, as this is unlikely to result in a reduction of the mortality, but will only aggravate existing cancrophobia in these strained patients.