Background: Prospective cohort study among close contacts of smear positive tuberculosis (TB) patients. Methods: Family and school contacts were followed up for 2 years or more after contact investigation. Tuberculin skin testing (TST) until positive reaction, interferon gamma releasing assay (IGRA, QuantiFERON® Gold In-Tube Assay), and chest X-ray were followed up at 3 - 6 months, 1 year, and 2 years after initial examination. Tracing of TB cases among close contacts was conducted through regular follow up examinations and monitoring by the TB surveillance system. Preventive treatment (PT) was recommended to the subjects indicated by the guidelines. Results: A total of 3,088 close contacts with a mean age of 15.2 ± 2.4 years old were recruited from 117 index cases during April 2008 and October 2011. Initial TST and IGRA positive rate was 23.0% (708) and 11.5% (355), respectively. Active TB was occurred in 27 cases (0.87%) including eight bacteriologically confirmed TB; 11 (4.2%) cases from initial TST and IGRA positive group (262), 11 (0.5%) cases from initial TST and IGRA negative group (2,272), three (0.7%) cases from initial TST positive but IGRA negative group (445), two (2.1%) cases from initial TST negative but IGRA positive group (93). Risk factors of the progression to TB were lower BMI [Odds ratio (OR); 4.70, 95% confidence interval (CI); 1.01-21.96], positive IGRA (OR; 11.66, 95%CI; 2.17, 62.75), and familial TB history (OR; 17.08, 95%CI; 1.91-152.60) by multivariate analysis. The risk was decreased in the cases completed PT compared to refusals among indicated by the guidelines (RR; 0.20, 95%CI; 0.05-0.85). Conclusions: Although overall progression to TB among close contacts was low, but higher in some specific groups.