OBJECTIVES: ;This study evaluated the effect of anti-thyroid drugs and thyroidectomy on response of hyperthyroidism to fixed doses of Radioactive Iodine Therapy (RAI) and the incidence of hypothyroidism at 6months post RAI therapy METHODS: ;A retrospective review of the medical records of 42 hyperthyroid patients treated with radioiodine to evaluate response rate of hyperthyroidism to two fixed dose regimens of 370 MBq (10 mCi) and 555 MBq (15 mCi) RAI therapy was carried out. The impacts of thyroidectomy and ant-thyroid drug pre-treatment were documented. The treatment goal is to cure hyperthyroidism by rendering the patient either euthyroid or hypothyroid, within 6months of single dose of 370 MBq (10 mCi) or 555 MBq (15 mCi) RAI therapy. Statistical analysis was with SPSS version 15.0 and the level of statistical significance was taken as P < 0.05 RESULTS: ;The response (i.e. hypothyroid and euthyroid) at 6months post RAI for both doses of radioiodine was 71.4%, and after re-treatment of 7 patients who were earlier hyperthyroid after 6months, the response rate soared to 95.2%. The incidence of hypothyroidism (TSH > 6.1 mIU/L) was 47.6% with patients who had received 370 MBq (10 mCi) and 38.1% with those that received 555 MBq (15 mCi) radioiodine therapy. The use of anti-thyroid drugs (carbimazole or methimazole only) as pre-treatment increased response to RAI; Propylthiouracil however blocked response to RAI therapy in one patient Thyroidectomy, either total or subtotal, increased the response to RAI treatment CONCLUSIONS: ;Radioactive iodine is highly effective for the treatment of Graves' hyperthyroidism, with a very high cure rate. Pretreatment with some anti-thyroid drugs protects against worsening of thyrotoxicosis after radioiodine and increases response to RAI therapy. Thyroidectomy increases the response to RAI treatment. However, the incidence of hypothyroidism should be anticipated and well prepared for as part of the treatment protocol