Objective: To investigate the factors affecting the prognosis of patients with medullary thyroid carcinoma (MTC). Methods: The data of 602 patients with definite pathological diagnosis of MTC were collected from SEER database within 2010 to 2014 by using SEER*Stat software. The survival rates of the patients were analyzed by Kaplan-Meier method and Log-rank test, and the risk factors for survival of the patients were determined by univariate analysis and multivariate Cox regression model. Results: Of the 602 patients, the mean survival time was (54.914±1.209) months, and the 1- and 3-year overall survival rate was 96.9% and 90.8%, respectively. The results of univariate analysis showed that age at diagnosis (χ2=33.232, P<0.001), sex (χ2=4.030, P<0.045), size of primary tumor (χ2=37.060, P<0.001), number of lesions (χ2=6.876, P=0.009), clinical stage (χ2=116.467, P<0.001), primary tumor stage (χ2=72.482, P<0.001), regional lymph node involvement (χ2=14.803, P<0.001), distant metastasis (χ2=94.976; P<0.001), surgical procedure (χ2=80.536, P<0.001) and number of positive lymph nodes (χ2=18.700, P<0.001) were significantly related to the survival rate of the patients. The results of multivariate Cox analysis revealed that age at diagnosis (HR=2.777, 95% CI=1.800–4.285, P<0.001), primary tumor stage (HR=1.675, 95% CI=1.289–2.176, P<0.001) and distant metastasis (HR=5.401, 95% CI=2.720–10.725, P<0.001) were independent risk factors for the prognosis of the patients. Conclusion: The clinical variables that include age at diagnosis, primary tumor stage and distant metastasis can be used as the independent predictive indicators for the prognosis of the MTC patients.