BACKGROUND: The prognostic role of lymph node metastases in well-differentiated thyroid carcinoma remains controversial. We investigated impact of lymph node involvement on survival in patients with well-differentiated thyroid cancer. METHODS: We queried the Surveillance, Epidemiology, and End Results registry for patients diagnosed with well-differentiated thyroid carcinoma between 1988 and 2003. Cases were stratified by age (<45 vs >/=45 years) and pathology (papillary/follicular). Four separate Cox regression models were developed to test the effects of demographic and clinical covariates on survival. RESULTS: We identified 33,088 patients. 30,504 patients (49% >/=45 years) had papillary carcinoma and 2,584 patients (55% >/=45 years) had follicular carcinoma. Age affected survival in all models (P < .001). In patients with papillary carcinoma <45 years, lymph node disease did not influence survival (P = .535), whereas in patients >/=45 years, lymph node involvement was associated with 46% increased risk of death (P < .001). In patients with follicular carcinoma, lymph node involvement conferred increased risk of death in both age groups (P </= .002). Effects of other covariates varied between models. CONCLUSION: Cervical lymph node metastases conferred independent risk in all patients with follicular carcinoma and in those patients with papillary carcinoma aged >/=45 years, but did not affect survival in patients with papillary carcinoma <45 years.