The material presented dates from a nationwide Cancer Registry, and covers all cases of papillary thyroid carcinoma (T.C.) diagnosed in Denmark from 1943 to 1968, including those based on postmortem examinations. Direct comparison with clinical data from hospitals elsewhere will therefore tend to show less favorable results. In general, Danish cases show a higher average age than those from American hospitals. For the younger age groups this may to some extent be explained by the fact that therapeutic x-irradiation of the thymus during childhood has never been practiced in Denmark. However, the later occurrence in life of Danish cases and the less favorable prognosis might suggest a failure to realize the malignant character of the lesion in the earlier part of its course, and a variable experience on the part of the surgeons and the variety of institutions from which the material was collected. The age-adjusted incidence rate, the mortality, and complications are discussed. It is concluded that the prognosis may be improved considerably by more extensive operations on the thyroid gland, avoiding complications such as paralysis of the recurrent laryngeal nerve and tetany. The surgical efforts should be supplemented with suppression of the TSH production. In the present retrospective study it was not possible to report 20- and 30-year survival rates. This is a task for the future, as is the planning of prospective studies which, in the case of a disease as rare as papillary T.C., should be established on an international basis.