The highest incidence of anaplastic thyroid carcinoma (ATC) has been reported in countries with endemic goiter, such as in Ecuador. In this country, ATC is the third most common histologic type of thyroid cancer, following papillary and follicular carcinoma. The aim of this study was to review the clinical presentation and the results of treatment of a large consecutive series of ATC patients treated at the oncological department of a general hospital in Quito, Ecuador. This is a retrospective study of 30 patients diagnosed with ATC at the Social Security Hospital, from 1982 to 1998. Symptomatic rapidly growing neck masses were generally present. All the patients had histological diagnosis of ATC. Two patients with pulmonary metastases and pleural effusion died before treatment could be instituted. Twenty-eight patients received at least one type of treatment: surgery, radiation therapy (RT), or chemotherapy (CT). The two most frequently employed therapeutic modalities were surgery followed by RT and/or CT in 14 patients and surgery alone in 9 patients. Surgery was performed in 23 patients but a complete resection was possible in only 14 patients. RT, postoperatively or alone, was given to 17 patients. Only 5 patients received doses ranging from 4,000 to 5,000 cGy and 4 patients more than 5,000 cGy. CT was administered to 17 patients. Doxorubicin alone was given to 10 patients and different combinations to the remaining patients. Local control was obtained in 8 of 14 complete resections. The prognostic value of the following parameters was studied by univariate analysis: duration of symptoms, size of the tumor, extent of glandular involvement, type of treatment, and surgical margins. A statistically longer survival was found in cases of differentiated carcinoma with areas of ATC or tumor limited to one lobe, those patients who received a complete treatment of chemotherapy, and those patients with tumors smaller than 10 cm and with duration of symptoms longer than 4 months. Longer mean survivals were seen in patients with longer duration of symptoms and smaller lesions. Five patients with focal anaplastic lesions within a differentiated thyroid carcinoma or a lesion limited to one lobe had a significant better survival (a mean of 20 months).