A 56-year-old woman presented with rapidly enlarging thyroid mass and deep anemia. There was no history of gastrointestinal bleeding, and endoscopic examinations of the gastrointestinal system were normal. Fine needle aspiration cytology from the thyroid nodule was suspicious. After blood transfusion, total thyroidectomy was performed. Postoperative histopathological examination of the specimen revealed hemangiosarcoma of the thyroid. After establishment of the diagnosis chemotherapy was started. But hemoglobin values decreased again and hepatosplenomegaly developed at the second month of surgery. Bone marrow aspiration cytology which was performed demonstrated the same tumoral cells infiltrating bone marrow. The patient died at 12th week after surgery. Thyroid hemangiosarcoma can metastasize to the bone marrow and anemia may be an indicator of the advanced disease. In the differential diagnosis of the anemia, bone marrow metastasis and bone marrow biopsy should be considered in suspected cases.