Law 100 introduced the Health Sector Reform in Colombia, a model of managed competition. This article addresses the effects of this model in terms of output and outcomes of TB control. Trends in main TB control indicators were analysed using secondary data sources, and 25 interviews were done with key informants from public and private insurers and provider institutions, and from the health directorate level. We found a deterioration in the performance of TB control: a decreasing number of BCG vaccine doses applied, a reduction in case finding and contacts identification, low cure rates and an increasing loss of follow up, which mainly affects poor people. Fragmentation occurred as the atomization and discontinuity of the technical processes took place, there was a lack of coordination, as well as a breakdown between individual and collective interventions, and the health information system began to disintegrate. The introduction of the Managed Competition (MC) in Colombia appeared to have adverse effects on TB control due to the dominance of the economic rationality in the health system and the weak state stewardship. Our recommendations are to restructure the reform's public health component, strengthen the technical capacity in public health of the state, mainly at the local and departmental levels, and to improve the health information system by reorienting its objectives to public health goals. Copyright © 2004 John Wiley & Sons, Ltd.