Differentiated thyroid carcinoma is a slow growing tumor with relative good prognosis. But locally advanced thyroid cancer with T4 or N1b is difficult to manage. Between June 1988 and April 1995, we resected 8 advanced thyroid cancers trans-sternally. All patients had direct mediastinal extension [T4 or mediastinal lymph node metastasis [N1b with airway obstruction or dysphagia. We operated all the patients by partial or total sternotomy for mediastinal dissection along with thyroidectomy and radical neck dissection. There were some acceptable morbidities but no operative mortality. Postoperative radioactive iodine therapy was followed without side effects. Follow-up survival period was between 11 months to 81 months with 2 late mortalities [17 month, 30 month . Although definite benefit for routine mediastinal dissection in thyroid cancer has not been established, in locally advanced cases impending airway obstruction or dysphagia who have questionable effect by radioactive iodine therapy alone, aggressive mediastinal mass dissection including lymph node metastasis has the significant role to prevent the patients from suffocation & dysphagia, and to enhance the effect of followed radioactive iodine tharapy.