Serum thyroglobulin (Tg) is the key parameter used in the follow-up of subjects with differentiated thyroid cancer (DTC). Current guidelines advise its measurement to take place when Thyrotropin (TSH) levels are >30 µU/ml (stimulated Tg) and when TSH < 0.1 µU/ml (suppressed Tg). Although stimulated Tg levels <1 ng/ml have been shown to display excellent prognosis, relapses may occur despite low Tg levels. Recently, very low cut-off levels of stimulated Tg have been proposed for determining the recurrence risk in these subjects. In this study, we aimed to assess the association between ablative stimulated Tg obtained before radioactive iodine ablation therapy (RAI) (ASTg) and late stimulated Tg obtained 6-12 months after primary therapy (LSTg) in a group of subjects with DTC. We also aimed to establish a cut-off level of Tg for recurrence.