The Authors emphasize the importance of preoperative aspiration cytology in the diagnosis of 5 medullary types out of 58 thyroid carcinomas observed in the Institute of Pathology of the Università Cattolica del S. Cuore of Rome in the period 1983-88. All the cases were diagnosed preoperatively by mean of a fine-needle aspiration cytological specimen; the case where morphological diagnosis was doubtful were studied with immunohistochemical techniques for calcitonin and CEA. Out of all cases, they report one case of multiple endocrine adenomatosis type II with medullary thyroid carcinoma and pheochromocytoma and another one with cervical node metastases without a clinically detectable thyroid swelling. Therefore, the authors propose the fine-needle aspiration cytology as a simple and important mean in the preoperative diagnostic procedure in case of medullary thyroid carcinoma.