Tuberculosis (TB) is a common cause of morbidity and mortality worldwide. The number of new cases continues to increase despite intense efforts to eradicate the disease. According to the World Health Organization, the global incidence rate of TB increased to 8.8 million cases in 2002 with a growth rate of 2.4% per year.1 In the United States, about half of the new cases occur in persons immigrating to this country.2 Treatment of persons with active TB is the number one priority targeted to prevent the spread of infection. A secondary priority, particularly in developed countries where there is a lower incidence of the disease, is the identification and treatment of persons with latent TB infection (LTBI).3 The majority of new cases of TB are derived from a pool of patients with LTBI. Thus, identifying and treating persons with latent infections is an important public health measure, since it not only prevents active TB from occurring in individuals with latent infection, but also prevents the interpersonal spread of the disease. Understanding the available tests and how to correctly interpret and apply the results is the first step in recognizing patients at risk and in providing appropriate treatment.