A summary of the clinical data of the 131I-thyroid function tests and the therapeutic results of 131I among the 2,658 patients of various thyroid diseases treated over the past 10 years from May 1960 to Oct. 1969 at the Radioisotope Clinci and Laboratory, SNUH were presented and discussed. 1) The patients examined consisted of 929 cases (34.9%) of diffuse toxic goiter, 762 cases (28.7%) of diffuse nontoxic goiter, 699 cases (26.3%) of nodular nontoxic goiter, 58 cases (2.2%) of nodular toxic goiter and 210 cases (7.9%) of hypothyroidism. 2) There were 300 (11.4%) male and 2358 (88.6%) female, showing a ratio of 1:8. 3) The majority of patients (79.1%) were in the 3rd-5th decade of their lives. 3) The normal ranges, diagnostic values of 131I uptake test, 48 hrs serum activity, BMR and main subjective symptoms of various thyroid diseases were discussed. 5) In the 579 patients among 867 cases with hyperthyroidism treated with 131I, 47.8% were confirmed to be cured completely after single therapeutic doses. 6) The complications of 131I therapy were discussed and myxedema had developed in 6.75% of our patients. 7) The results of 131I thyroid function tests were analysed among the 160 cases of thyroid diseases which were confirmed the diagnosis with histopathological measures.