Thyroid lipomatosis is a rare condition characterized by the presence of abundant mature adipose tissue in the thyroid gland. We herein report the case of a 43-year-old man with chronic renal failure caused by amyloidosis presenting with an asymmetrically enlarging thyroid gland. The patient's thyroid hormone levels were normal, and test results for thyroid autoantibodies were negative. A thyroid scan showed diffuse uptake of the radioisotope with a cold area in the left lobe. The pathology of the thyroidectomy material indicated thyroid lipomatosis, and minimal amyloid staining was noted around the thyroid follicles. Thyroid lipomatosis should therefore be kept in mind when making a differential diagnosis of fatty infiltration of amyloid goiter.