Fifty seven patients with differentiated thyroid carcinoma were performed radioactive iodine-131 whole body scans after administration of diagnostic dose $(2sim10;mCi)$ and therapeutic dose $(30sim150;mCi)$ within three months. We evaluated the state of radioactive iodine-131 uptakes in whole body scan to detect correct metastasis of thyroid carcinoma. The results are as follows: 1) In 20 of the 57 patients (35%), the therapeutic scan showed the additional uptakes that were not seen in the diagnostic scan. 2) In 9 (64.2%) of the 14 patients who had been received the thyroid ablation theraphy with I-131 previously, new additional lesions were found in the therapeutic scan but only 11 (25%) of the 32 patients who had not been received the thyroid ablation theraphy disclosed new uptake lesions (p < 0.01). 3) The additional uptake lesions of therapeutic scan were significantly more common in the bony metastatic foci (55.7%) than other areas (p < 0.01). In 11 (55%) of 20 patients, additional uptake regions were anterior neck areas (thyroid bed or regional lymph node). We conclude that diagnostic scan with $2sim5$ mCi I-131 is inadequate in evaluating residual iodine avid tissues of patients with thyroid carcinoma. Also post-theraphy I-131 whole body scan would be important to evaluate the correct staging and prognosis of thyroid carcinoma, and to follow-up patients.