Medullary thyroid cancer (MTC) is a rare cancer. There is a relative paucity of data over the last decade with regard to the prognosis of these patients. Therefore, the authors used the population-based Surveillance, Epidemiology, and End Results (SEER) registry to update what to their knowledge is one of the largest series of patients with MTC reported to date. All patients with a diagnosis of MTC with active follow-up in the SEER database from 1973 to 2002 were included. Univariate and multivariate regression analyses were used to assess the associations between demographic, clinical, and pathologic characteristics of patients and survival. A total of 1252 patients with MTC were identified over 29 years of follow-up. In all, 87% of patients were white and 60% were female, with a mean age of 50 years. Although many variables were significant on univariate analysis, SEER stage and age at diagnosis were found to be the strongest predictors of survival in the multivariate analysis. Prognosis was poor in patients with advanced disease (hazards ratio [HR], 4.47), or those age >65 years (HR, 6.55). Patients who underwent surgery fared better than those who did not. Overall, 51% of patients had less than the currently recommended treatment guidelines for MTC. Adjuvant radiation therapy was found to be independently associated with a decreased survival (HR, 1.65). Stage of disease and age at diagnosis were found to be the strongest predictors of survival for patients with MTC. To the authors' knowledge there has been no change in stage at diagnosis or a significant improvement in survival noted over the last 30 years. Many patients underwent surgery that was deemed less than optimal for stage of disease. (c) 2006 American Cancer Society.