Epidemiology started its work since 1968 BCG trial in tuberculosis in Chingelput, district. This area utilized as the population laboratory for the study of the epidemiology of Tuberculosis. After the BCG Trial, several disease prevalence surveys were undertaken by NIRT Epidemiology unit. The RNTCP was introduced in the BCG trial area in 1999. Disease Survey and Tuberculin survey are being carried out in the BCG trial area to study the impact of DOTS strategy (RNTCP) on the epidemiology of TB. Further, three repeat surveys were carried out in the same area. A case control study was done in 1998 to study the association between Tobacco smoking and Pulmonary TB. The epidemiology unit of TRC has also collaborated with National Tuberculosis Institute, Bangalore , in conducting a nation wide sample survey (tuberculin survey). Mortality surveys were completed in Andhra Pradesh and Orissa. Studies on mortality among cohorts of tuberculosis patients from Chennai Corporation and Thiruvallur district were completed. Following this, prevalence of tobacco use among the urban, semi-urban and rural areas around Chennai City were carried out. Further, in the subsequent disease surveys conducted in Chennai Metropolitan City, .the information on exposure to risk factors like smoking, alcohol consumption were collected to study the association between these behavioral risk factors with pulmonary TB.