Anaplastic thyroid carcinoma (ATC) is a rare disease that shows very aggressive behavior. Most ATCs arise from pre-existing thyroid carcinomas. However, anaplastic transformation occurring in metastatic cervical nodes is extremely rare. We report herein on 3 cases of anaplastic transformation of metastatic lateral cervical lymph nodes from primary papillary thyroid carcinoma (PTC), which happened long after the initial surgical treatment. All the patients died of disease within 4 months in spite of aggressive treatment for the lesions. Our experience supports that appropriate lymph node dissection is mandatory at the time of initial surgery even for differentiated thyroid carcinomas.