Insular thyroid carcinoma is a rare tumor originated in the epitelial cells of the thyroid gland, situated in an intermediate position between the well-differentiated and undifferentiated tumors. It was initially reported by Langhans in 1907 and later on studied in depth by Carcangiu in 1984, who described its anatomopathologic characteristics and reported a series of cases with an exclusive insular pattern and a more aggressive clinical outcome. Since then, it has also been called poorly differentiated carcinoma of the thyroid. It is a neoplasia with high risk of metastasis that is not as aggressive as the anaplastic thyroid carcinoma. Most clinicians recommend an intensive treatment that in some cases can prolong patient survival. In this module two cases with insular thyroid carcinoma are presented.