Aim: The aims of this audit were: To determine the proportion of hyperthyroid patients receiving I-131 therapy in whom treatment with a single fixed dose was successful, as defined by the achievement of euthyroidism or hypothyroidism 6-months after the therapy; To identify patients in whom treatment was not successful and a second dose needed; And, if possible, to establish the factors associated with treatment failure. Methods: A single observer reviewed the records of all patients who received I-131 therapy for hyperthyroidism between 23rd April 2010 and 23rd November 2017 in conjunction with their pre and post treatment thyroid function tests. Results of their thyroid ultrasound were retrieved and documented. The images of their Tc-99m sodium pertechnetate thyroid scans were also retrieved and reprocessed. Results: The records of 409 patients treated between April 2010 and November 2017 were retrieved. 223 (63%) patients were referred by the endocrine clinic at Groote Schuur hospital (GSH. Of the 409 patients, 56 (14%) patients that were excluded because their post therapy records were not available for analysis. Majority of our patients were females 310 (88%). Patients between the ages of 15 and 45 years are more likely to present with Grave’s disease while those aged more than 45 years presented with toxic multinodular gland (p=0.000). Patients that presented between the ages of 15 and 45 years are more likely to have moderately increased pretreatment FT4 (12-51 mmol/L) (p=0.002). We administered a radioiodine therapy dose of 456.6±54.8 MBq (Mean ± SD) to these 409 patients. Among the 353 patients, with complete records, 314(89%) achieved cure at some stage after receiving one dose of RAI; 239(76%) achieving cure ≤ 6 months of therapy and 75(24%) patients after 6 months. In our audit the patients who failed to achieve cure following the first RAI therapy appeared to be younger (median(interquartile range) age 39(16), p= 0.03), have severe hyperthyroidism as demonstrated by higher pre-treatment FT4 (median(interquartile range) 27 pmol/L(30.6), p= 0.05) and high pertechnetate uptake (median(interquartile range) uptake 9.9%(14), p= 0.002) on thyroid scintigraphy. CONCLUSION Our audit showed RAI therapy was found to be successful in 68% of patients at 6 month and 89% at a year. A second therapy with radioactive iodine would be indicated in 32% of patients, as these patients have not achieved cure at 6 months. Patients presenting with severe thyrotoxicity are likely to require more than one RAI therapy. Due to major deficiencies in referral, record keeping and follow up, other factors responsible for treatment were not be able to be evaluated. Based on these findings, suggested areas for further research are: should patients with severe hyperthyroidism be considered for pretreatment with antithyroid medication prior to RAI; would a one year follow up after radioiodine therapy be considered before second RAI. Now that the deficiencies in our current practice have been identified and suggestions put forward to address these deficiencies, a follow up audit would be needed.