Follow-up of patients who undergo a total thyroidectomy is performed with thyroglobulin (Tg), and antithyroglobulin antibodies (AbTg). The objective of RAI adjuvant therapy is to negativize Tg to undetectable levels to ease the follow-up. The objective of this study was to evaluate the correlation of serum Tg values measured 2 weeks after surgery with the Tg value prior to RAI adjuvant therapy in order to define its utility as a reliable predictor of pretherapy Tg and as a potential predictor to avoid RAI adjuvant therapy.Retrospective analysis of a cohort recruited prospectively. Adult patients with thyroid carcinoma who underwent total thyroidectomy and classified as intermediate or high risk by ATA guidelines. All patients were left without levothyroxine support after surgery and for at least two weeks. We measured biochemical markers two-four weeks after thyroidectomy and before and after RAI.We included 75 patients. Thirty-three (44.0%) patients were classified as ATA high risk. In the post-RAI scan, only 1 (1.3%) showed distant metastases. The comparison between early postoperative and pretherapy Tg values showed that Tg decreased or remained stable at postoperative levels in 75 patients (100%).Postoperative Tg measurements are a reliable marker of pretherapy Tg levels in patients with intermediate- and high-risk thyroid carcinoma who are candidates for RAI adjuvant therapy. These results need correlation with outcomes and response to therapy in high-risk patients.