This prospective study evaluated the recurrence rate in 715 patients with differentiated thyroid cancer who had no evidence of persistent disease after total thyroidectomy and lymph node dissection in 94% of them followed up by radioiodine ablation (30-100 mCi) and assessed the predictive value of the initial thyroglobulin (Tg) levels for detecting recurrence, both during levothyroxine (LT4) treatment and after TSH stimulation.