Objective The use of tumor necrosis factor inhibitors (anti-TNF) has a risk of activating latent tuberculosis infection (LTBI). This study was performed to investigate LTBI according to tuberculin skin test (TST) size and to determine the frequency of tuberculosis (TB) in bacillus Calmette-Guerin (BCG)-vaccinated children receiving anti-TNF treatment for rheumatological disease. Materials and Methods The study consisted of 559 children. Information on demographics, anti-TNF agents, TST size, and isoniazid (INH) prophylaxis was recorded. Patients (n = 254) with TST size >= 5 mm were divided into three groups according to TST size and INH prophylaxis: group 1, TST size 5 to 9 mm and no INH prophylaxis; group 2, TST size 5 to 9 mm with INH prophylaxis; and group 3, TST size >= 10 mm with INH prophylaxis. Results The 559 patients comprised 314 (56.3%) females and 245 (43.6%) males; they had a mean age of 13.1 +/- 4.1 years. The mean TST size in all patients was 4.2 +/- 4.7 mm. Group 1 consisted of 76 (29.9%) patients, group 2 consisted of 88 (34.6%) patients, and group 3 consisted of 90 (35.4%) patients. The mean TST sizes for the three groups were 6.8 +/- 3.1 mm, 7.2 +/- 3.2 mm, and 13.9 +/- 2.8 mm, respectively. New TB was diagnosed in only two (0.35%) patients. Both of them were in group 3. Conclusions A TST size of >= 10 mm in BCG-vaccinated children receiving anti-TNF treatment may distinguish children at high risk for reactivation of LTBI.