There is no established chemotherapy for anaplastic thyroid cancer. We conducted a prospective feasibility study at a single center to explore the antitumor activity of docetaxel against anaplastic thyroid cancer. Docetaxel was administered intravenously at a dose of 60 mg/m(2) over the course of 1 h every 3 weeks in patients with anaplastic thyroid cancer who had received no prior chemotherapy. A total of seven patients with anaplastic thyroid cancer were enrolled over the course of 30 months and received docetaxel. The treatment response was complete response in one patient, stable disease in two and progressive disease in four. The response rate was 14%, and the disease control rate (complete response plus stable disease) was 43%. The median time to progression was 6 weeks (range, 1-50). Toxicity was tolerable. Docetaxel could be an effective drug for the treatment of anaplastic thyroid cancer, with tolerable toxicity.