Between 1970 and 1987, 20,028 fine needle aspirates (FNA) of the thyroid have been examined in the Department of Pathology of the University of Innsbruck, Austria. During this period 92 cases of anaplastic carcinoma and 16 cases of malignant haemangioendothelioma (MHE) of the thyroid were diagnosed. Forty-three out of these 108 highly malignant tumours of the thyroid underwent FNA pre-operatively (39.1%). Thirty-seven FNA contained numerous cells of a highly malignant tumour. Five specimens (11.8%) contained only necrotic material and inflammatory cells. In one case of an anaplastic carcinoma no malignant cells could be demonstrated in FNA. We conclude that pre-operative FNA of highly malignant thyroid tumours may contribute substantially to subsequent clinical management.