Though survival for well-differentiated thyroid cancer is very good, specific populations suffer greater recurrence and mortality. Defining these cohorts can significantly influence prognosis and extent of treatment. This study, using a large, multi-institutional database, seeks to determine how the presence of lymph node disease in patients with well-differentiated thyroid cancer affects outcome. The Surveillance, Epidemiology, and End Results (SEER) database is a large-scale sample of 14 per cent of the U.S. population. It was used to identify patients with papillary and follicular thyroid carcinomas and identify the prognostic implications of lymph node metastasis. Additional factors, including presence of metastasis, age, and tumor size, were compared using multivariate and chi2 analyses. Of 19,918 patients identified, lymph node status was known for 9,904 (49.7%). On multivariate analysis, age > 45 years, presence of distant metastasis, large tumor size, and lymph node involvement significantly predicted poor outcome. Overall survival at 14 years was 82 per cent for node negative and 79 per cent for node positive patients (P < 0.05). This study shows that the survival of patients with well-differentiated thyroid cancer is adversely affected by lymph node metastases. The optimum treatment for this cohort needs further delineation, as particular populations are at greater risk of recurrence and death.