The well differentiated thyroid carcinomas are uncommon but are increasing in frequency. This increase may be related to the recognition that even low doses of irradiation to the thyroid may be carcinogenic with a latency period of 10, 20 or more years to clinical tumor expression. Although unproven for human cancers, elevated TSH levels will enhance irradiation-associated tumor development in animal models. Currently, a large portion of the population is at an increased risk of developing thyroid cancer because of head and neck irradiation received from 1920 to 1950 for various benign conditions or more recently for the treatment of lymphoma or carcinoma. Whether these individuals should receive thyroid hormone suppression of TSH is not known but careful yearly evaluation is essential followed by open surgical biopsy should a nodule develop. Treatment of the well differentiated thyroid carcinoma is controversial due to a lack of adequate long-term, controlled trials. Based on current data, it is the author's opinion that surgery should in most cases be followed with radioactive iodine ablation of all remaining tissue which can concentrate iodine followed by lifelong thyroid hormone replacement sufficient to correct hypothyroidism and suppress thyroid stimulating hormone. All patients require close follow-up with examination and, possibly, imaging for 20 or more years.