The aim of this study was to analyze the disposition of radioiodine used for the ablation of thyroid remnants after radical surgery for a differentiated thyroid carcinoma in a patient on chronic hemodialysis in order to deliver the optimal (131)I dose to improve the healing rate in these rare cases and to serve as a useful reference to other health care professionals who might face a similar dilemma. A 50 mCi dose of (131)I was administered orally and dialysis sessions were performed 24, 72 and 144 h after therapy. Patient effluent dialyzate waste samples were collected and blood radioactivity analyses were performed at each dialysis session. The (131)I disposition half-life was 2.7 +/- 0.8 h. The amounts of remnant radioactivity in total body patient were 58.7, 38.9 and 27.1%, respectively, after each of the three dialysis sessions and the effective period calculated was 1.4 days. The extents of water purification in blood were 69.7, 47.9 and 22.7% at the beginning of each dialysis and 37.7, 42.8 and 18.1% at the end of each dialysis. Effective periods of radioiodine for thyroid cancer in a patient on hemodialysis resulted in rapid iodine clearance, thereby reducing the effective radiation dose and promoting the need to use larger treatment doses. Hemodialysis was safe and effective during treatment with radioiodine.