Despite the fact that 15% to 20% of sarcomas occur in the head and neck and 80% in adults, only 0.014% are primary thyroid leiomyosarcomas. To the best of our knowledge, only 16 cases have been reported around the world, none in South America. Cytologic diagnosis is challenging and these tumors may be mistaken by more common ones such as anaplastic or medullary carcinomas. The treatment of choice for thyroid leiomyosarcomas is not well established yet because of its poor prognosis. Radical surgery associated with chemoradiotherapy has not been effective and did not improve survival rates. The authors report a case of primary thyroid leiomyosarcoma in a young male, who has been submitted to total thyroidectomy and selective neck dissection. Extensive literature review was performed by the authors. The patient received adjuvant radiotherapy, presenting good postoperative course. After four years evolution, there was no local recurrence or distant metastasis.
