The understanding of the prognostic factors and risk groups is crucial in the management of well differentiated thyroid cancer. The important prognostic factors are age, grade of tumor, extrathyroidal extension, size of tumor, and distant metastases. Based on these prognostic factors, patients can be divided into low-, intermediate-, and high-risk groups. The treatment decisions should be based on risk group analysis. Extent of thyroidectomy and adjuvant therapy can be based on the risk group analysis. The histopathologic studies are very important to distinguish well differentiated from the tall cell, insular, and poorly differentiated thyroid cancer.