Radionuclide therapy has a proven place in the management of patients with thyroid disease. Iodine-131 therapy has been established as both successful and safe in treating patients with thyrotoxicosis and thyroid malignancy. Protocols for patient treatment are now standardised, although some variation in practice exists across Europe. There remains much confusion as to which patients should be selected for treatment with radio-iodine for thyrotoxicosis and what dose should be administered. A review of the literature reveals that many of the theoretical hazards of treatment with radio-iodine have not been encountered despite many years of usage. New therapies for medullary thyroid cancer are now being evaluated and recent promising developments are discussed in detail.