Background: In general, the prognosis in patients with well differentiated thyroid carcinoma (WDTC) is excellent. However, there are small cohorts of patients who experience a more aggressive form of disease which is often associated with certain poor prognostic factors. Identifying these patients at an early stage is imperative for guiding treatment decisions. The purpose of the work is to study the cumulative survival of patients with WDTC, depending on a number of clinical and biological characteristics of tumors. Methods: A retrospective cohort study of patients operated on WDTC in the period from 1995 to 2015 (5526 people). Each patient was analyzed according to age, gender, tumor size and characteristics of the TNM (7 editions), clinical stage, volume of surgery, number of points on the MACIS scale, risk group, number of courses of radioiodine treatment, result treatment and the term of postoperative observation. The construction of cumulative survival curves was made according to the Kaplan-Meier approach. To compare the cumulative survival index value in groups, the non-parametric Log-rank test was used. Results: The most unfavorable factors of the prognosis for patients with WDTC are such integrated indicators as the stage of disease IVb and IVc, as well as tumors of the T4b category. It is also unfavorable to recognize the age of patients over 60 years, the presence of distant metastases, the stage of disease IVa, the category of carcinomas T4a and the size of the tumor more than 40 mm. Other prognostic factors (invasion, multifocal tumor growth, metastasis of carcinoma to the lymph nodes, male sex, post-operative relapse), although they are probable predictive factors, but have somewhat less significance in analyzing the prognosis of survival of patients. Conclusion: Understanding the importance of certain prognostic factors of survival is extremely necessary, since they are the only indicators of the effectiveness of the diagnostic, medical and organizational work will reduce the number of patients who require aggressive treatments and, consequently, increase the duration and quality of their postoperative life.