A 65-year-old woman with follicular thyroid carcinoma was treated with total thyroidectomy and radioiodine ablative therapy with 3943 MBq (107 mCi) I-131. Whole-body planar scintigraphy revealed an increased radioactivity in the upper pole of the right kidney, suggesting an unusual case of renal metastasis of a follicular thyroid carcinoma. SPECT/CT using a low dose CT protocol was performed as well as ultrasound. Although ultrasound revealed a cyst in the upper pole of the right kidney, the low dose CT was not helpful to differentiate a cyst from a solid renal tumor. Pyelocaliceal diverticulum may be considered as a pitfall in I-131 scintigraphy.