Background: The tuberculin skin test (TST) has limitations in diagnosing a latent tuberculosis infection (LTBI). The interferon-gamma release assay (IGRA) was introduced to middle- and high-school students since 2009 by the Korea Centers for Disease Control and Prevention. The aim was to evaluate the utility of IGRA in diagnosing LTBI in middle- and high-school students. Methods: From August 2007 to July 2009, among suspected LTBI students showing TST induration with a 10 mm diameter and over with a normal chest x-ray in school students of Jeju city, 341 students underwent a Quanti FERON-TB Gold In-Tube (QFT-IT) test to confirm LTBI. Results: From 348 students showing a positive TST, a QFT-IT test was carried out on 341 students. The positive QFT-IT rate was 52.8% (=180/341). The positive QFT-IT rate was higher in high-school boys with a 15~19 mm diameter of induration in TST. Conclusion: With the introduction of IGRA for diagnosing LTBI in middle- and high-school students, approximately 47% of students who show a TST induration with a 10 mm diameter and over can avoid taking unnecessary preventive chemotherapy. These results suggest that IGRA is useful for diagnosing and controlling LTBI in Korean students.