Well-differentiated thyroid carcinoma (TC), as papillary and follicular carcinoma, usually follows a relatively benign course after total thyroidectomy and thyroid remnant ablation with 131I. In contrast, anaplastic TC or undifferentiated TC, also derived from the thyroid follicular epithelium, refers to one of the more aggressive human malignancies, which have lost most or all characteristics of the tissue from which it originated. Rapid tumor growth presages early mortality unless combined therapy is aggressively pursued. Definitive curative approach does not exist for most patients. The best approach is still aggressive surgery combined with the associated use of new chemotherapies associated with local external beam radiotherapy.