A demographic, computerized model of the tuberculosis situation in a community is described with regard to its structure and modus operandi. In systems analysis of tuberculosis control programs, the model will help to clarify the expected effects of various measures taken by the public health authorities, and thus guide the authorities toward the most effective use of available resources. Lack of quantitative information about some aspects of the tuberculosis situation militates against forecasts that are precise in absolute terms, but it is contended that this might not prevent accuracy in relative terms. The tuberculosis situation in Thailand is selected to illustrate the application of the model to real situations, and to show how various, potentially possible control programs may be evaluated with regard to their costs and the expected benefits accruing from them.