Anaplastic thyroid carcinoma. review of six patients Background: Anaplastic Thyroid Carcinoma corresponds 2 to 5% of all thyroid cancers. It affects mainly women in the sixth or seventh decade of life, appearing as a hard, fast growing cervical mass that is adhered to surrounding structures. Treatment includes surgery, chemotherapy and radiotherapy. Aim: to report a series of patients with anaplastic thyroid carcinoma. Patients and Methods: Review of medical records of patients with anaplastic thyroid cancer operated between 2002 and 2008. Results: The records of six patients aged 46 to 82 years (four males), were retrieved. A bilateral total thyroidectomy was performed in four patients. Two patients required tracheostomy during the postoperative period. Mean hospital stay was six days. None received neoadjuvant or adjuvant radio-chemotherapy. Three patients died within one month of the operation. The rest died at 115, 184 and 283 days after surgery. Conclusions: All these patients were diagnosed in advanced stages of the disease, a fact that can explain the dismal evolution observed.