Iodine deficiency disease (IDD) is common in China.An universal salt iodization (USI) program has been implemented by the Chinese government since 1996. As a result, the goiter rate in 8- to 10-year old children decreased from 20.4% in 1995 to 5.8% in 2002.1 But the adverse effects of iodine excess such as iodine-induced hyperthyroidism, iodine-induced goiters, iodine-induced hypothyroidism, etc. have become a great concern to healthcare professionals as well as the general population. The impact of USI on antithyroid drugs (ATDs) might become a potential challenge to address. With a special grant from the Department of Disease Control, the Health Ministry of China, we conducted a prospective study on the effects of USI on ATDs at the thyroid section of the Endocrinology Clinic of Peking Union Medical College Hospital (PUMCH), Beijing.