65 cases of hemangioendothelioma (HE) of the thyroid were accepted as such after control of slides of surgical or autopsy specimen or both. In a few of the more recent cases material could be examined by electron microscope and in some the search for factor VIII-related antigen (FVIIIRAG) was carried out. The demonstration of Weibel-Palade bodies in tumour cells in two cases and the evidence of FVIIIRAG in tumour cells of at least two cases, including primary tumour and distant metastasis, finally show, that the hemangioendothelioma of the thyroid is not simply an anaplastic carcinoma with some peculiar features; at least some of these tumours are true endotheliomas. The proposal that the term hemangioendothelioma be eliminated from the classification of thyroid tumours is therefore unfounded.