Differentiated thyroid cancer comprises papillary, mixed papillary-follicular and follicular adenocarcinomas. They are mostly hormone-sensitive and respond to thyroid-stimulating hormone (TSH) suppression. The standard treatment is total thyroidectomy. I-131 therapy and thyroid hormone suppression therapy. Adjuvant external radiotherapy is discussed controversially Most authors recommend adjuvant external radiotherapy for extracapsular tumor extension. Decision on an individual basis should be made for patients with lymph node involvement. In the case of incomplete surgical resection, external radiotherapy should be applied if second surgery is not possible. For medullary thyroid cancer, external beam radiotherapy seems to be beneficial for patients with surgically inaccessible disease, with microscopic residual or gross tumor after surgery, with recurrent locoregional disease, or with surgically unmanageable metastases. Patients suffering from anaplastic thyroid cancer should receive combined treatment consisting of extensive surgery, external irradiation with total doses up to 60 Gy, and chemotherapy. The combined treatment modality leads to higher local control rates and prolongs survival.