The clinical data of a patient with differentiated thyroid carcinoma(DTC)who developed physiological thymic uptake after postoperative iodine-131(131I)therapy were analyzed,and the 3-year follow-up changes in the patient's condition were reviewed.Combined with the literatures and the diagnosis and treatment process,the causes of possible false positives in whole-body scans after iodine therapy for DTC and the mechanism,clinical features,and identification methods of benign thymic 131I uptake were discussed to improve clinicians' understanding and diagnostic ability regarding such conditions and avoid unnecessary multiple iodine treatments.The patient,a 28-year-old female,showed mediastinal imaging after the first 131I treatment,with more pronounced mediastinal iodine uptake during the second treatment.SPECT/CT localized the uptake to enlarged thymus tissue.The stimulated thyroglobulin(Tg)levels before two 131I treatments were high but gradually decreased.Apart from thymic uptake,no other examination evidence suggested DTC metastases.Subsequent follow-up for 3 years showed no pathological changes in the thymus,confirming physiological thymic uptake.Thymic 131I uptake is a common cause of false-positive whole-body scans in post-thyroidectomy patients.When post-131I therapy whole-body imaging shows only mediastinal uptake,especially in the young patients undergoing multiple 131I treatments where thymic 131I uptake intensity increases with successive treatments,even with elevated Tg levels,comprehensive use of imaging results such as SPECT/CT is essential to determine if it is normal thymus,thereby avoiding unnecessary repeated therapies.