A 30 year-old female patient with papillary thyroid carcinoma received her fifth radioiodine ablation therapy after the subtotal thyroidectomy. The scan, which was peformed one week after the last therapy, revealed residual uptake in the thyroid bed and uptake in the anterior mediastinum suggesting metastasis. However, further evaluation of the thorax with chest CT and camera-based FDG PET confirmed normal thymus without metastatic focus. Occasionally thymus remains intact in adult and has avidity for I-131 and FDG. Therefore, normal thymus (instead of metastasis) should be considered in patients with well differentiated thyroid carcinoma and anterior mediastinal radioiodine uptake.