Differentiated thyroid carcinoma is a relatively indolent disease. Despite the usually favorable prognosis, differentiated thyroid cancer is fatal in some patients. In the past, treatment strategies were often based upon incomplete knowledge or inaccurate assumptions regarding the significance of the presenting characteristics of the tumor and patient. More recently, several large retrospective reviews have analyzed various presenting factors and have identified those that have prognostic significance and those that do not. Significant prognostic factors are age, primary tumor size, histology, grade, local tumor extension, and M stage. N stage appears to be a significant factor in older patients but not in younger patients. Gender, focality, and a history of prior irradiation are not significant prognostic factors. Using this knowledge, patients can be grouped into low, intermediate, and high risk groups. Prognostic factor and risk group analysis has facilitated the development of more rational treatment algorithms. Low risk patients can usually be treated with lobectomy and suppression therapy. For high risk patients, total thyroidectomy and adjuvant radioiodine is advocated. Treatment for patients in the intermediate risk group should be individualized. Prognostic factor and risk group analysis makes a selective approach to differentiated thyroid cancer possible. Such an approach can spare many patients the morbidity and expense of unnecessarily aggressive treatment without compromising outcome.