The authors report a case of anaplastic thyroid carcinoma which was treated with chemotherapy and radiotherapy and proved to achieve pathological CR (complete response) after a radical operation. A 53-year-old female presented with a mass of about 4 cm in diameter arising from the left lobe of her thyroid and surrounding her cervical esophagus. Pre-operative aspiration cytology and open biopsy revealed the tumor was a giant cell anaplastic carcinoma. There was no sign of distant metastasis. Two cycles of chemotherapy were very effective in treating the tumor but regrowth appeared to occur during hyperfractionated radiotherapy. A radical operation, including a resection of the larynx, cervical trachea and esophagus, was successfully performed and no living cancer cells, only granulation and necrosis, were observed in the operation specimen. The patient has been alive for over 2 years since without any evidence of recurrence.