Objective: To determine the prevalence of thyroglossal tract thyroid tissue on SPECT/CT and to assess the contribution of this tissue to total neck radioactive iodine (RAI) activity in patients given 131I ablation therapy after total thyroidectomy for thyroid cancer. Patients and Methods: Eighty-three consecutive patients with thyroid cancer treated with total thyroidectomy underwent whole-body planar and SPECT/CT imaging of the neck following initial RAI ablation. On SPECT/CT, thyroglossal tract thyroid tissue was defined as RAI in the anterior neck, superior to the thyroid bed in close proximity to the midline without evidence of localization to lymph nodes. Quantification was performed using region of interest analysis on planar imaging following localization on SPECT/CT. SPECT/CT, and planar images were classified by two reviewers as positive, negative or equivocal with interobserver agreement quantified using a Kappa score. Disagreement was resolved using a third reviewer. Results: Thyroglossal tract thyroid tissue was present in 39/83 (47 ; 95 CI: 36-58 ) patients on SPECT/CT. In these 39 patients, this tissue contributed to a significant amount of total neck activity (median = 50 ; IQR 19-74 ). Interobserver agreement for the presence of thyroglossal tract thyroid tissue was substantial on SPECT/CT (Kappa = 0?73) and fair on planar imaging (Kappa = 0?31). Conclusion: Thyroglossal tract thyroid tissue was present in one half of our study population and contributed to a significant amount of total neck RAI activity. Given the high prevalence of this tissue, our results suggest that total neck RAI activity on planar imaging may not be suitable to assess the completeness of thyroid bed surgery.