Oh CM, Lim J, Jung YS, et al. - This research sought to explore the trends in thyroid cancer incidence by the histologic type, cancer stage, and age group and explored possible factors that affected thyroid cancer trends. Between 1999 and 2016, a descriptive epidemiological study was performed using the national cancer registry data and cause of death data in South Korea. Using Segi's world standard population, age‐standardized rates were estimated. They used Joinpoint regression analysis to ascertain the changing point of thyroid cancer trends according to histologic type; Surveillance, Epidemiology, and End Results summary stage; and age groups by gender. The results revealed that the incidence of thyroid cancer began declining from 2012 before the debates for overdiagnosis of thyroid cancer began in 2014. For thyroid nodule examinations, changes in guidelines may have affected this inflection point. Furthermore, the debates for overdiagnosis of thyroid cancer may have accelerated the decline in thyroid cancer.