Tuberculosis is a serious health problem in India, but because of inadequate facilities for diagnosis in many parts of the country clinical data are incomplete. However, data on prevalence are available from a few sample surveys conducted in the general population during the last two decades. The study reported here provides information on the incidence of infection and disease as well as on the source and fate of cases. The information was obtained by means of surveys, repeated at intervals during 1961-68 in a randomly selected rural population of South India. In each survey, a tuberculin test was given and X-ray and sputum examinations were made. There were virtually no tuberculosis control facilities in the study area, since this was not covered by the national tuberculosis programme at the time.The annual rate of tuberculous infection in previously uninfected children and in adults was found to be about 1%. The incidence of tuberculosis (confirmed by culture) was about 1 per thousand (excluding children below the age of 5 years). About 30% of newly detected cases came from the population uninfected at an earlier survey. The prevalence of disease was four times as high as the incidence. Among cases found in the initial survey one-half died within 5 years and one-fifth continued to excrete bacilli after 5 years. Both infection and disease tended to decline during the observation period, though in an uneven manner that does not permit extrapolation. There was no evidence of an increase in drug-resistance among newly diagnosed cases. The findings of the study could be used in developing epidemetric models to predict the tuberculosis problem and to assess tuberculosis control measures applied in the community.