Anaplastic thyroid carcinoma (ATC) is an aggressive malignancy and characterized by spreading to regional lymph nodes and distant metastases, but we were unable to find a previous report of simultaneous metastases of transformed ATC to either the small intestine or thoracic esophagus in the English language literature. A 60-year-old man suffered from well-differentiated thyroid carcinoma and underwent total thyroidectomy. Eight years later, local recurrence of thyroid cancer showed intense fluorodeoxyglucose/positron emission tomography (FDG-PET) uptake at the paratracheal region, which was suspected as a remnant tumor of the thyroid that transformed from differentiated to ATC. At that time, the patient underwent resection of the small intestine to remove an abdominal mass and consequently developed stenosis of the thoracic esophagus caused by the esophageal tumor. Histological scrutiny of specimens from both tumors in the small intestine and thoracic esophagus demonstrated the same pattern as that of undifferentiated carcinoma. Regarding histological verification and a change in the FDP-PET uptake level, it is strongly possible that our case demonstrated coincident metastases of ATC to both the small intestine and esophagus. In conclusion and to the best of our knowledge, this report is the first to present evidence suggesting that ATC has the potential to metastasize to any organs, including the digestive tract.