A patient known to be suffering from Gardner's syndrome who developed carcinoma of the thyroid gland is presented. A review of the literature reveals that this relationship is not fortuitous and that it has the following characteristics: female predominance (89%), youth (< 30 years in 78%), papillary form (88%), multicentricity (70%) and thyroid carcinoma preceding diagnosis of hereditary polyposis in 30%. Hereditary polyposis patients affected by familial polyposis coli are at significant risk of developing extracolonic malignant tumours, and require life-long surveillance. Palpation of the thyroid gland and possibly ultrasound examination of the neck should be part of the routine follow up of these patients.