This paper addresses the role of information in health policy reform. It recognizes that reform can be based on data, but that there are other influences on health policy. The steps involved in making policy, including problem identification, comparison of solutions, policy adoption, implementation, and amendment, all require information. When information is unavailable for any of these steps, the policy process sometimes proceeds without it. The policy makers must make difficult choices regarding the potential benefit of comprehensive information to the policy outcome versus the potential drawbacks, in terms of time and cost, of seeking the missing information. Different areas where data are needed within health policy are enumerated, as are sources of health policy data, and examples of strategies are given. Finally, three case studies are presented, highlighting the use of information in policy making. The National Epidemiology Board in Thailand commissioned studies by experts on relevant policy topics. It had a substantial impact on changing policies in the areas of AIDS control, iodine deficiency, essential drugs and vaccination. The attempt at decentralizing health administration to the province level in Papua New Guinea is the second example presented. At the time of the evaluation, this effort had not yet attained its objectives of improving the health of the people, nor had it reduced costs or lessened inequity among regions. If this reform had been tested in a pilot project, its problems may have been discovered at an earlier stage of implementation when they would have been easier to correct. The final case concerns the UNICEF child survival interventions during the 1980s. These interventions were chosen based on cost-effectiveness analysis and were successfully implemented. The use of cost-effectiveness analysis in prioritizing interventions is one example of the way in which information can improve policy and health outcomes.