Tuberculosis has shown a resurgence in nonendemic populations in recent years, a phenomenon that has been attributed to factors such as increased migration and the human immunodeficiency virus epidemic. Although the thorax is most frequently involved, tuberculosis may involve any of a number of organ systems (eg, the respiratory, cardiac, central nervous, musculoskeletal, gastrointestinal, and genitourinary systems), and timely diagnosis of the disease is paramount, since delayed treatment is associated with severe morbidity. Unfortunately, a history of infection with or exposure to tuberculosis may or may not be present, and evidence of active tuberculosis is present in less than 50% of cases. A negative tuberculin skin test does not in itself exclude infection. Furthermore, the clinical and radiologic features of tuberculosis may mimic those of many other diseases. Therefore, although in many cases biopsy or culture specimens are required to make the definitive diagnosis, it is imperative that radiologists and clinicians understand the typical distribution, patterns, and imaging manifestations of tuberculosis. (c) RSNA, 2007.