A 42-year old white female with a primary Malignant Fibrous Histiocytoma (MFH) is described. The patient was examined for a "cold" nodule of the thyroid diagnosed five years previously. The patient had been on L-thyroxine therapy for three years which was discontinued by the patient 18 months prior to the present visit. Fine needle aspiration of the thyroid nodule indicated a low differentiated neoplasm with some mucous production. The patient underwent total thyroidectomy and excision of the infiltrated part of the anterior cervical muscles. The histology showed MFH on the thyroid, an extremely rare primary localization of this neoplasm. For the subsequent 8 years, the patient was well with no evidence of recurrence or metastasis. Afterwards, she developed a fast growing nodal structure on the mitral valve, leading to its surgical replacement. This operation was followed by several thromboembolic episodes (pulmonary and cerebral) which led to her death 10 years after thyroidectomy.