The aim of this study is to analyze the impact of combined treatment (thyroidectomy and radiotherapy and radioactive iodine treatment) on patients’ long-term survival with medullary thyroid carcinoma. This is a retrospective study of 59 patients treated from 1977 to 2006 for medullary carcinoma at the Institute of Oncology in Vilnius, Lithuania. Survival was estimated by the Kaplan-Meier method. Univariate and multivariate Cox proportional hazard models were used to explore the association of prognostic factors with long-term survival. The survival of MTC patients was 88.0% (95% CI 68.0–88.9), 67.9% (95% CI 52.3–79.4) and 60.5% (95% CI 43.2–74.0), respectively, 5, 10 and 15 years after diagnosis. In survival analysis, only the type of surgery and lymph node involvement were found to be significant prognostic factors. The results of this study suggest that treatment with radioiodine and external beam radiotherapy do not improve significantly the long-term survival of surgically treated MTC patients.