The worldwide incidence of thyroid cancer has doubled during the last 30–40 years. Mainly the proportion of papillary cancers has increased, whereas follicular and anaplastic cancers have decreased in frequency. This trend is presumably related to an improvement of nutritional iodine supply. According to autopsy studies, the prevalence of occult thyroid cancer is high in relation to the intensity of the histological work-up (up to 35 %); however, only 1 in every 10,000 of these microcarcinomas is clinically relevant. The most important etiological factor for thyroid cancer is radiation exposure in childhood. The prognosis of differentiated thyroid cancer with 10-year survival rates in a range of 95% for papillary and 85% for follicular cancers is very good. In contrast, the prognosis of anaplastic cancer with 10-year survival rates of less than 15% is extremely bad. The prognosis is determined by the patient’s age at the time of diagnosis, tumor growth beyond the thyroid capsule, distant metastases and—with some restrictions—lymph node metastases. In this context it should be taken into consideration that age is not a prognostically independent factor.