In this study, the lifetime risk of reactivation tuberculosis among persons in the United States who have had a positive tuberculin skin test was estimated from published data. The lifetime risk is 20 percent or higher among persons with skin-test induration of 10 mm or greater and either human immunodeficiency virus infection or evidence of old, healed tuberculosis. The lifetime risk of reactivation tuberculosis is 20 percent or higher among some groups. Once the transmission of Mycobacterium tuberculosis from persons with active tuberculosis has been controlled in a population, the focus of tuberculosis control shifts to the prevention of active tuberculosis among persons with latent tuberculosis infection — those who have a positive tuberculin skin test but no evidence of active disease. Tuberculosis in this subpopulation results from the reactivation of previously controlled infection and is termed reactivation tuberculosis. The prevention of reactivation tuberculosis through the treatment of latent tuberculosis infection is a major goal of the national strategy for eliminating tuberculosis in the United States. 1 – 3 Unfortunately, the treatment of latent . . .