Insular carcinoma of the thyroid is a rare thyroid malignancy, and this was named in 1984 by Carcangiu when he described its characteristic histology. Histologically, insular carcinoma is characterized by uniform cells arranged in distinct nests or an insular pattern that contain variable numbers of small follicles. Clinically and morphologically, it is considered to be in an intermediate position between well-differentiated carcinoma of the thyroid (papillary or follicular) and undifferentiated or anaplastic carcinoma of the thyroid. This thyroid malignancy is distinctive, aggressive and often lethal. However, most authors believe it to be an independent entity. The prognosis of this tumor is worse than that of classic differentiated thyroid carcinoma, and most authors advise aggressive therapy, which can achieve pro-longed survival in some cases. We describe here a patient (a 42 years-old woman) who was managed with completion thyroidectomy after unilateral lobectomy of the thyroid with confirmation of the permanent pathology as insular carcinoma. I-131 ablation (175 mCi) was performed on the remnant thyroid tissues after follow-up of I~131 whole-body scanning.