Objective: A new risk stratification system was proposed to estimate the risk of recurrence in patients with differentiated thyroid carcinoma (DTC) using the response to initial therapy. Here, we describe the modified dynamic risk stratification system, which takes into consideration the status of serum anti-Tg antibody (TgAb), and validate this system for assessing the risk of recurrence in patients with DTC. Patients and methods: Patients who underwent total thyroidectomy with radioiodine remnant ablation due to DTC between 2000 and 2005 were included. We classified patients into four groups based on the response to the initial therapy ('excellent', 'acceptable', 'biochemical incomplete', and 'structural incomplete' response). Results: The median follow-up period of 715 patients with DTC was 8 years. The response to initial therapy was an important risk predictor for recurrent/persistent DTC. The relative risks (95% CI) of recurrence were 16.5 (6.3-43.0) in the 'acceptable response ' group, 41.3 (15.4-110.8) in the 'biochemical incomplete response' group, and 281.2 (112.9-700.5) in the 'structural incomplete response' group compared with the 'excellent response' group (P!0.001, P!0.001, and P!0.001 respectively). The disease-free survival rate of the 'excellent response' group to initial therapy was 98.3% whereas that of the 'structural incomplete response' group was only 6.8%. Conclusions: Our study validates the usefulness of the modified dynamic risk stratification system including the status of serum TgAb for predicting recurrent/persistent disease in patients with DTC. Personalized risk assessment using the response to initial therapy could be useful for the follow-up and management of patients with DTC.