Papillary thyroid carcinoma accounts for over 90% of all thyroid cancers. As radio-sensitivity is generally low and no effective anticancer drug exists, surgery still plays a central role in treatment of patients with papillary thyroid carcinoma. Radioactive- iodine ablation and thyroid-stimulating hormone suppression are sometimes employed as postoperative adjuvant therapies; however, they are not particularly effective for highly malignant tumors. In order to establish an appropriate treatment strategy, it is important to consider the risk of recurrence and cancer death for the individual patient, according to the adequate risk-group definition. Non-surgical observation can be applied to patients with the lowest-risk cancers: namely, asymptomatic papillary microcarcinoma. For patients with high-risk cancers, indication and extent of surgery should be determined after evaluating whether local control of the disease has a significant advantage for each patient's survival and quality of life. Anaplastic thyroid carcinoma is uncommon, but is one of the most lethal neoplasms in humans. Although anaplastic thyroid carcinoma generally has a dismal prognosis, some patients survive for a fairly long time after multidisciplinary treatment, including surgery, external radiation and chemotherapy.