Background and aims: Thyroid cancer is a malignancy of the endocrine system that its incidence has been raising steadily in many parts of the world. Regarding to existence of many factors affecting on disease-free survival in patients suffering from thyroid cancer, this study was aimed to identify this factors.

Methods: In this historical cohort study, 785 cases of differentiated thyroid cancer patients referred nuclear medicine wards of Imam Reza and Ghaem hospitals, Mashhad during the
1978-2012 were assessed. The follow-up of all patients was performed through periodic visits and telephone. The effect of various demographic and clinical factors on disease free survival of patients was evaluated using Weibull regression model.

Results: The median disease-free survival time of patients was resulted in 15±1.05 years. Evaluating the clinical and pathological features using univariate analysis showed that the impact of gender, age at diagnosis, type of cancer, stage of cancer, type of treatment, the primary of Thymoglobulin, size of motor, the status of involved Lymph nodes and status of metastasis, incomplete surgery had a significant association with disease free survival of patients(P<0.05). Moreover, in the multivariate case, size of motor, the status of involved Lymph nodes, status of metastasis and age at diagnosis was significant and had a significant association with disease free survival of patients (P<0.05).

Conclusion: Regarding to the numerous factors that impact the risk of recurrence and  affect the status of metastasis, size of motor and the status of involved Lymph nodes and  age at diagnosis at the moderate status, it seems that those with distant metastases as well as those in the fourth stages and aged over 45 years are at greater risk of recurrence.