In 1999, the SouthKorean government initiated a national cancer screening program, which led to increased high-resolution ultrasonography screening for thyroid cancer. Consequently,thyroid cancer incidence increased from7.2 per 100000 population in 1999 to 68.7 per 100000 population in 2011, and most patients received surgery. However,many screen-detected cancers were small and likely indolent. Concerns about overdiagnosis were raised beginning in2012, and ultrasonographic screening was discouraged in 2014, leading to decreased incidence of thyroid cancer and thyroidectomies. We assessed the changes in incidence rates of postoperative hypoparathyroidism, a complication of thyroidectomy, between 2007 and 2016.