The efficacy of targeted monotherapy for BRAF V600E-positive anaplastic thyroid carcinomas (ATC) is not established. We report 2 cases of BRAF V600E-positive ATC treated with a BRAF inhibitor. A 49-year-old woman with a T4bN1bM0 ATC manifested symptomatic metastatic disease 8 weeks after radical chemoradiotherapy. Within 1 month of BRAF inhibitor monotherapy, a complete symptomatic response was observed, with FDG-PET scan confirming metabolic and radiologic response. Treatment was terminated after 3 months because of disease progression. The patient died 11 months after primary diagnosis. A 67-year-old man received first-line BRAF inhibitor for a T4aN1bM0 ATC. Within 10 days of treatment his pain had stabilized and his tumor had clinically halved in size. Stable disease was achieved for 11 weeks but the patient died 11 months after diagnosis because of disease progression. BRAF inhibitor monotherapy in ATC may obtain clinical benefit of short duration. Upfront combination therapy should be investigated in this patient subgroup.