In a group of 840 patients with thyroid carcinoma the authors found pulmonary metastases in 123 patients, i. e. in 14.6%. In 78 pulmonary metastases were the only remote ones, in the remainder they were combined also with other remote metastates, almost always bone metastases. Cases of "pure" pulmonary metastases were found in the whole group without a proved relationship to age and histology, with a slight prdominance of men, while in patients with a combination of pulmonary and bone metastases follicular carcinoma predominates and it is found mainly in patients of more advanced age. The biological behaviour of these two groups differs completely, and this should be taken into account in the international TNM classification. When investigating the biological properties of thyroid carcinoma, we evaluated in detail in a recent publication (15) bone metastases. As all remote metastases of thyroid carcinoma are included according to the classification of WHO under the common sign M1 (9), we wanted to compare some factors in the incidence of pulmonary and bone metastases.