We report a 22-year-old female who was diagnosed as familial adenomatous polyposis (FAP) associated with thyroid carcinoma. Total thyroidectomy and bilateral neck lymph nodes dissection were performed. Gardner's syndrome was pointed out after an investigation of her family. Total colectomy and ileo-rectal anastomosis were carried out. Colon cancer was not found pathologically. We reviewed 10 cases of FAP with thyroid carcinoma in Japan. Ten out of 11 cases including this patient were female. Thus it is important to pay careful attention to the presence of thyroid carcinoma in the case of FAP or Gardner's syndrome.