Anaplastic thyroid carcinoma (ATC) is the most aggressive of thyroid cancers whose treatment is not yet established and mortality is extremely high. Recent in vitro studies have shown that valproic acid (VA), a newly identified histone deacetilase (HDAC) inhibitor, induces apoptosis, modulates differentiation gene expression of thyroid tumors and enhances the sensitivity of anaplastic cancer cell lines to doxorubicin. We report a case of successful treatment of anaplastic thyroid carcinoma with a combination of oral valproic acid, chemotherapy consisting of cisplatin and doxorubicin, external and intra-operative radiation and surgery. Tumor volume decreased by 50.7% under CT measurement and 44.6% under sonogram measurement over the course of the treatment. No significant rebound of tumor size was observed between each cycle of chemotherapy. Serial cytology performed via fine needle aspiration (FNA) presented a rapidly changing profile of cell types, starting with anaplastic and proceeding through increasingly well differentiated presentations. Only microscopic remnants of ATC cells were found in the histological examination of the resected thyroid. Ga scintigraphy and whole body PET scan six months after surgery revealed no evidence of recurrence or metastasis. As of Nov. 22, 2008, the patient is alive and disease free two years after diagnosis.