Background The treatment for thyroid cancer is surgical. However, some patients do not undergo operations because of comorbidities or other reasons. There is little information about the prognosis of these patients. The aim of the present study was to describe patients with well differentiated thyroid carcinoma who did not undergo surgical treatment and to identify differences in prognostic variables and survival compared with patients treated surgically. Methods We conducted a retrospective review of a prospective cohort collected by the National Cancer Institute obtained from the Surveillance, Epidemiology and End Results (SEER) Program. All patient fi les with a diagnosis of thyroid cancer were selected (38,493 cases). Finally, 12,416 cases were used for the analysis. Treatment was divided into surgical or nonsurgical groups. Five-year survival rates were estimated and classifi ed by the SEER stage. Results Eighty-six patients did not receive surgical treatment. These patients were older, had more advanced tumours and their treatment was less associated with complementary radiotherapy. Five-year overall survival rates were 96.7% for surgical patients vs. 56.8% for nonsurgical patients (p<0.001). The overall survival in the nonsurgery group for localised tumours decreased 14.9%, for regional tumours decreased 49.9% and for distant tumours decreased 61.8%. Discussion The patients who did not undergo surgical treatment showed less than 5-year overall survival. The SEER database does not offer information about comorbidities that could explain these differences.