Introduction: mixed medullary-follicular carcinoma of the thyroid with pleomorphic pattern is an uncommon malignant epithelial tumor characterized by clinical and immunohistochemical features of both follicular and parafollicular thyroidal C cells. Material and methods: we describe a rare case of this type of tumor observed in a 56 year old woman, undergone total thyroidectomy for suspected thyroid carcinoma, without lymph node metastasis. Preoperative basal calcitonin levels were in the limits, while thyroglobulin resulted increased. Presence of the latter suggests a potential usefulness of radioiodine therapy as an additional therapeutic tool for this type of tumor. Results: histological and immunohistochemical findings we re surprising showing characteristic patterns and thyroglobulin and calcitonin positivity. After postoperative diagnosis the patient undergone specific endocrine and scintigraphic tests. Conclusions: early diagnosis of a mixed medullary-follicular thyroid carcinoma is essential, considering its special t h e ra py and negative prognosis. In fact it constitutes another clinicopathologic entity, different from typical medullary thyroid carcinoma and it’s associated with a more favourable clinical course than the form e r. A precise diagnosis of this uncommon variety of medullary carcinoma of the thyroid is fundamental for an accurate treatment of the patient, but also for familiar genetic screening excluding MEN II syndromes. A radical surgical therapy plays a key-role for the treatment and the follow-up of this rare tumoral entity.