Radioiodine has been known as an important and safe armamentarium in the diagnosis and treatment of differentiated thyroid cancer (DTC) for more than 70 years. The 2015 guidelines from the American Thyroid Association (ATA) for adults with thyroid nodules and DTC seem to be the most comprehensive guidelines in the thyroid cancer field. The 2015 ATA guidelines provided an advance in evidence-based management of DTC, and resulted in a significant change in the patterns of practice regarding the application of the radioiodine. However, the 2015 ATA guidelines also provoked much controversy because a substantial portion of the recommendations announced were not based on sufficiently strong evidence. While the number of radioiodine administrations in Korea in the year of 2018 has decreased to a level less than 50% of that in 2013, in this review, we address some of the current issues and controversies regarding the application of radioiodine for the diagnosis, ablation and treatment of DTC, especially related to the 2015 ATA guidelines. Possible strategies for the achievement of better quality in radioiodine imaging and improvement in treatment efficiency that can be used in the near future are also discussed here.