South Korea is operating a flexible quarantine management system which is based on the results of epidemiological investigations of patients arriving from overseas with coronavirus disease-19 (COVID-19), and closely monitoring COVID-19 outbreaks. South Korea has designated countries with a localized, high prevalence of infection as “quarantine inspection required areas” and has reinforced quarantine measures by applying special immigration procedures for people entering South Korea. Furthermore, South Korea also provides information on international travel history of entrants (who are South Korean citizens and foreign nationals) to all medical institutions, through the smart quarantine information system. On March 11th 2020, the World Health Organization characterized COVID-19 as a pandemic. Inevitably, the number of patients from overseas with COVID-19 (based on 10,000 people entering South Korea), increased to 10 cases in the second week of March, 37 cases in the third week, and 67.7 cases in the fourth week. However, after enforcing quarantine strengthening measures, and with a decrease in the number of people entering the country, the number of cases decreased to 52.0 in the first week of April.