The incidence of thyroid cancer has been increasing in Korea as well as in many countries. This is mainly due to the early detection of papillary thyroid microcarcinoma less than 1 cm in diameter with a high-resolution ultrasonography. Because of the unique Korean medical environment, its incidence is abruptly increasing in Korea. Many experts have emphasized that the early detection cannot completely explain the observed increase in thyroid cancer. Therefore, other possible explanations should be explored. Unnecessary diagnosis and excessive treatment should be avoided. If unreasonable regulations are applied, they could do more harm than good. In terms of screening efficacy, the National Evidence-based Healthcare Collaborating Agency in conjunction with Korean Thyroid Association concluded in 2013 that evidence was insufficient to recommend for or against ultrasonography screening for thyroid cancer. If a patient incidentally finds a tumor on the thyroid, a physician should manage the patient according to the guidelines. The guidelines should be developed based on evidence-based medical decisions for patients, not on economic efficacy.