[Medullary carcinoma of the thyroid. Observation of a case]

A case of medullary carcinoma of the thyroid is reported, particular attention being paid to preoperative diagnostic problems. The importance of cytological examination carried out with fine needle acupuncture is also stressed. The anatomopathological and clinical features are outlined, special mention being made of the neoplasia's frequent hormonal secretion and its possible familial nature.