The aim of this study was to determine the relationship between residual radiation dose in thyroid cancer patients treated with high doses of I-131 [150-200 millicurie (mCi)] before discharge from Songklanagarind Hospital and exposure dose of I-131. This report was a retrospective analysis of data from 102 patients who received high dose I-131 therapy between February 2010 and February 2011. The relationship between the residual dose and exposure dose rate at 1 meter was y=592.94x+0.1931 {y=residual dose before discharge (mCi) and x=dose rate at 1 meter before discharge [millisievert per hour] (mSv/h)}. Six groups of patients were divided by residual radiation dose. In the group that had a residual dose of less than or equal to 7 mCi, accumulated dose to an individual at 30 centimeters was not greater than 5 millisievert (mSv). In the group that had a residual dose greater than 7 mCi, accumulated dose to an individual had likely received a dose at 30 centimeters greater than 5 mSv, which exceeded the dose limit for public members. Thus, awareness about radiation to other individuals must be continually performed. In the group of patients that had a residual dose greater than 7-10, 10-15, 15-20 and 20-30 mCi radiation precautions should be taken for 3, 6, 10 and 13 days, respectively. In the group of patients presenting with greater than 30 mCi, the release of patients may be possible in suitable situations, with 17 days radiation precaution.