Thyroid dysfunction following radioiodine for Graves' disease is common, potentially detrimental and avoidable. A variety of clinical strategies are employed in the post-radioiodine era util the patient is on a stable thyroid hormone replacement regimen, which include the use of anti-thyroid drugs, antithyroid drugs with thyroxine, early thyroxine replacement and watchful monitoring until the onset of hypothyroidism. Which of these is most effective in avoiding dysthyroidism, is unknown. This study aims to address this lack of evidence. It will focus on Graves' disease as this is the commonest cause of thyrotoxicosis and the commonest indication for RI therapy. It will provide an insight into potential strategies for improving important clinical outcomes.

Inclusion Criteria:

• Out-patients 18 years of age or over, who have given written informed consent to participate in the study
• Diagnosed with Graves' disease
• Received radioiodine for treatment of Graves' disease
• Had a minimum of 12 months follow-up after RI
• Most recent RI dose 5 years ago or less at the time of enrollment

Exclusion Criteria:

• Patients unable to give informed consent
• Age 17 years or younger
• Cause of thyrotoxicosis other than Graves' disease
• Patients who have had more than one dose of radioiodine can only be included in the study once, using data pertaining to their most recent treatment episode.
• Patients who might not adequately understand verbal explanations or written information given in English, or who have special communication needs

Adult patients with a history of Graves' disease treated with radioiodine