Radioiodine therapy is an established mode of treatment of thyrotoxicosis with large range of etiologies. This study was carried out to assess the clinical outcome one year after administration of radioiodine therapy and also to identify whether any clinical features affect disease presentation and its response to treatment. Retrospective observational study was conducted in the nuclear medicine department of a multi-speciality hospital in which the records of 70 hyperthyroid patients were reviewed who were treated with the first dose of radioiodine during the inclusive period of August 2011 to August 2012. Among the 62 patients who completed follow-up, 24.3% of patients were euthyroid, 54.3% was hypothyroid while persistence or reoccurence of hypothyroidism was seen only in 10% of patients. The incidence of hypothyroidism was 38.5% in first trimester, 12.8% in second trimester, and 2.8% in third trimester. There was no significant difference in the response rate to different doses of radioiodine treatment groups, age, gender, pretreatments with antithyroid drugs and its duration and presence of goiter and ophthalmopathy(p>0.05). The fixed dose RAI therapy was very effective treatment for patients with hyperthyroidism and has a high success rate. A total 88.7% of patients are successfully treated and only 11.8% is still hyperthyroid which suggest that a second dose is necessary in these patients. Hence it was proved that radioactive iodine treatment is an effective treatment modality for definitive treatment of hyperthyroidism with long term cure. The analysed demographic factors do not affect the outcome of I131 therapy in hyperthyroidism.A single fixed dose of radioiodine therapy is a simple, safe and effective treatment for hyperthyroidism.