The authors report a case of medullary carcinoma of the thyroid diagnosed at the 2nd Surgery Clinic of IRCCS Policlinico "San Matteo" in Pavia in a series of 600 cases of thyroid pathology. Having emphasised the rarity of this pathology, the authors report the characteristic pathological aspects. They also outline the clinical signs leading to suspected diagnosis, illustrate the diagnostic techniques used to achieve an early diagnosis and underline the importance of the tumour markers CT and CEA. They identify radical surgery, total thyroidectomy with MND lymphadenectomy, as the therapy of choice, followed by accurate and careful monitoring with a view to ensuring an early diagnosis of renewed disease or recidivation.