A retrospective review of a consecutive series of 931 previously untreated patients with differentiated thyroid carcinoma treated over a 50-year period was undertaken to analyze prognostic factors. Data pertaining to demographic status, clinical, operative, and pathologic findings, and survival were analyzed. Univariate statistical analysis was performed based on the Kaplan-Meier method and the log-rank test. Multivariate analysis was performed to assess the independent effect of these variables using the Cox model. There were 630 female and 301 male patients, with an average age of 43 years. A total of 532 patients were younger than 45 years. Seven hundred thirty-one patients had either pure or mixed papillary carcinoma, and 200 had follicular carcinoma. In 153 patients, lesions were larger than 4 cm. Extrathyroidal extension was noted in 71 patients. Multifocal lesions were present in 159 patients. Regional lymph node metastasis was present on admission in 451 patients, and distant metastases were noted on presentation in 45 patients. Determinate survival for all patients was 87% at 10 years. Favorable prognostic factors using univariate analysis included female gender, multifocal primary tumors, and regional lymph node metastases. Adverse prognostic factors included age over 45 years, follicular histology, extrathyroidal extension, tumor size exceeding 4 cm, and the presence of distant metastases. On multivariate analysis, the only factors that affected the prognosis were patient age, histology, tumor size, extrathyroidal extension, and distant metastases. These observations support findings of reports from the Mayo Clinic and Lahey Clinic regarding the significance of prognostic factors for differentiated carcinoma of the thyroid gland.