Eighty-four cases of spindle and giant cell carcinoma of the thyroid were reviewed. This is a swiftly growing, and rapidly fatal neoplasm that generally develops in the elderly. Treatment of this disease was generally unsuccessful with a 7.1% five-year survival rate and a mean survival period of 6.2 months from the time of tissue diagnosis. In the majority of cases, areas of well-differentiated thyroid carcinoma could be identified, supporting the concept that spindle and giant cell carcinoma results from the transformation of preexisting well-differentiated thyroid carcinoma. Because of the aggressive biologic activity of this neoplasm, we treat all cases as disseminated disease at the time of presentation. Our best therapeutic results have been obtained with a combination of surgery, irradiation, and chemotherapy; however, these results still leave much to be desired. Patients with only small foci of spindle and giant cell carcinoma, at the time of diagnosis, may have a better chance of prolonged survival.