Purpose of review: Review of the management decisions that must be made by the endocrinologist during the use of radioactive iodine (RAI) therapy of hyperthyroidism and differentiated thyroid cancer.

Recent findings: Since the 1940s radioactive (131)I (RAI) therapy has been a major component of the treatment of hyperthyroidism and differentiated thyroid cancer. RAI is the most common definitive treatment of hyperthyroidism. Pretherapy decisions including use of antithyroid medication and low-iodine diet will be discussed with the relevant supportive literature. The method of semi-quantitative calculation used for RAI treatment of hyperthyroidism will be described. Evidence-based guideline for the management of differentiated thyroid cancer by the American Thyroid Association, new drug development and recent randomized controlled trials have changed current practice of how RAI is used for remnant ablation and adjuvant therapy of differentiated thyroid cancer.

Summary: RAI is a common tool for the endocrinologist in the management of hyperthyroidism and differentiated thyroid cancer. Review of the management decisions and practice of RAI therapy will educate the endocrinologist of the literature supporting current RAI use in hyperthyroidism and new developments in limiting the radiation exposure to the patients with differentiated thyroid cancer.