Intervention and cost durations were life long. TB prevention for men aged 20, recently infected with tubercle bacillus and thus at high risk was a dominant strategy versus no intervention yielding positive life year gained and savings of resources (costs and benefits discounted at 5%). TB prevention for men aged 55, with no risk factors other than long term presence of tubercle bacillus (low risk) yielded 11,135 per life-year gained (costs and benefits discounted at 5%) and 629 (costs and benefits not discounted). Incremental cost per life saved for: TB prevention for men aged 55, with no risk factors other than long term presence of tubercle bacillus (low risk) was 30878 (costs discounted at 5%) and 5131 (costs not discounted). TB prevention for men aged 55, with no risk factors other than long term presence of tubercle bacillus (low risk) yielded 10,196 per QALY gained (costs and benefits discounted at 5%). Sensitive parameters for TB prevention for men aged 55, with no risk factors other than long term presence of tubercle bacillus (low risk) were isoniazid hepatitis mortality (a side-effect more common in the elderly); cost and effectiveness of isoniazid chemoprophylaxis. The range of incremental cost per life year for: TB prevention for men aged 55, with no risk factors other than long term presence of tubercle bacillus (low risk) was 11,135 (baseline, costs and benefits discounted at 5%), with lowest value 425, and highest value 78,056. With extra health costs following survival: Cost/Life saved was 41800 (costs discounted at 5%), andcost/life year, was 15100 (costs and benefits discounted at 5%).