A number of histologic variants of well-differentiated papillary carcinoma have been found to be associated with more aggressive tumor behavior. Tall cell, columnar cell, diffuse sclerosing, solid/trabecular, and insular variants of well-differentiated papillary thyroid cancer are all potentially more aggressive than conventional papillary thyroid cancer. When subjected to multivariate analysis, however, evidence that the histologic subtype of tumor is an independent predictor of outcome is weak. Rather, the aggressive variants tend to present with features recognized by other staging systems as associated with a worse prognosis, including higher histologic grade, extracapsular spread, large tumor size, and the presence of distant metastases. Prognosis is directly related to the presence of these features. The state of our knowledge is limited by the relatively small number of cases that have been studied. The presence of an aggressive variant of papillary carcinoma should alert the surgeon that he is dealing with a potentially aggressive tumor. Clinical treatment decisions should be based on the stage of the disease, influenced by the knowledge that the aggressive variants tend to be associated with higher risk factors. The surgeon must be prepared to perform at the first, or second stage, a total thyroidectomy, central compartment neck dissection, additional lymphadenectomy, and/or resection of invaded surrounding structures, and search for distant metastasis. Postoperative radioactive iodine should generally be administered for these variants as they will generally be intermediate to advanced tumors. The tall cell variant is often refractory to such treatment but may be susceptible to treatment targeted against BRAF mutation. External beam irradiation may be used in cases of incomplete resection.