The objective of this study is to estimate the incidence of active tuberculosis in patients with inflammatory diseases receiving tumor necrosis factor-alpha (TNF-alpha) antagonists and to figure out the characteristics of patients who develop tuberculosis. 702 patients with different inflammatory diseases receiving TNF-alpha antagonists were followed up from August 2005 to July 2008 at our department of chest disease. All patients had tuberculin skin test (TST) and postero-anterior chest radiograph (CXR) prior to anti TNF-alpha antagonist treatment. All patients with a TST result a parts per thousand yen5 mm or fibrotic lesions on CXR were administered chemoprophylaxis with isoniazid (INH) for 9 months. 6 (0.85%) patients developed active tuberculosis (4 pulmonary and 2 extrapulmonary) during the follow-up period. TST was found to be positive in 434 (61.8%) of the patients. Patients, who were already on immunosuppressive therapy and who were not, were compared for the difference in their TST results and no statistically significant difference was found. Chemoprophylaxis was administered overall to 583 (83.0%) patients among which 31 (5.3%) developed hepatotoxicity. Of the patients who developed active tuberculosis, all were decided to receive INH chemoprophylaxis, however, only three of them adhered proper treatment. Diagnostic accuracy of TST for detecting latent tuberculosis is high among patients with inflammatory diseases even in the setting of immunosuppression. The risk of development of active TB is increased in this group of patients despite chemoprophylaxis, but this risk remains within the acceptable limits even in a moderate-tuberculosis incidence country, if proper chemoprophylaxis regimen is adhered.