Carcinoma of the thyroid is usually delineated as a cold defect on images with radioiodine and Tc-99m per-technetate. However, several cases that showed an accumulation of Tc-99m pertechnetate in thyroid carcinoma or in their metastases, but did not show any accumulation of radioiodine, have been reported. This paper presents a rare case of an advanced follicular adenocarcinoma of the thyroid that accumulated both Tc-99m pertechnetate and I-131. In this 41-year-old male patient, there were two primary foci in the thyroid; one occupied the whole left lobe with extension to the mediastinum and the other located in the lower part of the right lobe. In addition, there was a lymph node metastasis in the upper mediastinum adjacent to the left lobe. On images with both I-131 and Tc-99m pertechnetate, the tumor in the left lobe and the metastatic lymph node were delineated, but the tumor in the right lobe was not. Accumulation of Tc-99m pertechnetate in the lower part of the tumor of the left lobe was more distinct than that of I-131. Therefore, it is considered that despite similar histologic findings the trapping ability of the cancerous tissue differed from area to area.