Thyrotoxicosis is a common endocrine disorder. When untreated, it leads to congestive heart failure, arrhythmias and premature death. There appear to be ethnic differences in the incidence, severity and presentation of thyrotoxicosis, although there is little published data to confirm this. Maori appear to be disproportionately over-represented in patients referred with thyrotoxicosis and have more severe disease. In addition, for Maori and Pacific peoples a single dose of radioactive iodine is less likely to be curative. The reasons for these apparent differences are unknown. The objective of this research is to confirm whether there are ethnic differences in the presentation and treatment outcome of thyrotoxicosis. We plan a prospective observational study to assess ethnic differences in the presentation, severity and response to treatment of all new patients referred with thyrotoxicosis. Results from this research may identify factors which enable us to individualise therapy for thyrotoxicosis and reduce disparities in outcome.