The study was undertaken in order to estimate the radiation doses, that patients from Iran who received Na(131)I for the treatment of differentiated thyroid carcinoma (DTC) emit to their environment and also in order to evaluate the instructions given to these patients after being released from the nuclear medicine department. In 29 patients with DTC following thyroidectomy and immediately after the administration of therapeutic Na(131)I for the ablation of the thyroid remnants, the dose rates from the (131)I radioactivity emitted by these patients was measured at 3 meters. Also in these patients the dose rates from the (131)I were measured before they left the nuclear medicine department, at distances of 0.5 m, 1 m, and 3 m. The urine of these patients was collected for up to 3 days after (131)I administration. Results are as follows: The maximum dose received by the nursing staff was 1.6 mSv/week, less than the dose recommended by the International Committee for Radiation Protection (ICRP). The dose received by family members, as calculated on the basis of the time average dose rate on day 3 after the administration of (131)I was 46.3, 24.63, and 14.78 mSv/h at distances of 0.5, 1, and 3 m respectively. These results indicate that family members should take into consideration the duration and the distance of being in close contact with the above patients. The time-rate curve of urinary excretion of radioactivity in all patients showed multiple peaks due to the retention and redistribution of (131)I within the body and the enterohepatic cycle of radioiodinated thyroid hormones.