Thyroid cancer is one of the rarest forms of cancer, yet there are wide variations in the degree of malignancy, ranging from the most rapidly fatal to the relatively benign. This is almost entirely dependent on the histological type. Generally speaking, data available on changing trends of incidence and mortality are subject to reservation, dependent on the degree to which they have been influenced by changing diagnostic criteria and the precision of histopathological description. Nevertheless, there is evidence that mortality is slowly decreasing, while incidence is slowly increasing. The purpose of this review is to try to interpret the temporal trends of incidence and mortality rates for thyroid carcinoma in the last 3 decades in light of the problems arising from changes in diagnostic standards and histological classification regarding thyroid neoplasms. Attention is also drawn to the implications, from a public health viewpoint, of the present intensive detection and treatment of occult thyroid carcinomas.