Summary: Objective: We report a case of anaplastic thyroid carcinoma (ATC) with local recurrence and distant metastasis that responded very well to treatment with lenvatinib, a new molecular-targeted anticancer drug. Case Report: A 91-year-old Japanese woman presented with a 5-month history of a painless mass in her left anterior neck. She had a past history of total thyroidectomy and neck dissection for papillary carcinoma of the thyroid. Here she underwent neck dissection, and the histopathological diagnosis was lymph node metastasis of papillary carcinoma with anaplastic transformation. Five months later, a cervical lymph node swelled up again. Computed tomography demonstrated an enhanced mass in the neck and multiple nodules in both lungs. Recurrent ATC with multiple lung metastases was diagnosed, and molecular-targeted therapy with lenvatinib was initiated. The neck tumor reduced in 1 week, and the pulmonary nodules became completely hollow within 1 month. However, we had to discontinue lenvatinib because of severe side effects including high blood pressure, hypocalcemia, and hypoalbuminemia. Soon after discontinuation, the side effects subsided, but the tumor rapidly regrew. The patient died of lymphangiosis carcinomatosa 6 days after discontinuation. Conclusion: Although recent advances in molecular-targeted therapy have provided powerful cancer therapy tools, the negative side of this therapy must be addressed.