Integrated Management of Childhood Illness (IMCI) has been adopted by over 80 countries as a strategy for reducing child mortality and improving child health and development. It includes complementary interventions designed to address the major causes of child mortality at community, health facility, and health system levels. The Multi-Country Evaluation of IMCI Effectiveness, Cost and Impact (IMCI-MCE) is a global evaluation to determine the impact of IMCI on health outcomes and its cost-effectiveness. The MCE is coordinated by the Department of Child and Adolescent Health and Development of the World Health Organization. MCE studies are under way in Bangladesh, Brazil, Peru, Tanzania and Uganda. In Tanzania, the IMCI-MCE study uses a non-randomized observational design comparing four neighbouring districts, two of which have been implementing IMCI in conjunction with evidence-based planning and expenditure mapping at district level since 1997, and two of which began IMCI implementation in 2002. In these four districts, child health and child survival are documented at household level through cross-sectional, before-and-after surveys and through longitudinal demographic surveillance respectively. Here we present results of a survey conducted in August 2000 in stratified random samples of government health facilities to compare the quality of case-management and health systems support in IMCI and comparison districts. The results indicate that children in IMCI districts received better care than children in comparison districts: their health problems were more thoroughly assessed, they were more likely to be diagnosed and treated correctly as determined through a gold-standard re-examination, and the caretakers of the children were more likely to receive appropriate counselling and reported higher levels of knowledge about how to care for their sick children. There were few differences between IMCI and comparison districts in the level of health system support for child health services at facility level. This study suggests that IMCI, in the presence of a decentralized health system with practical health system planning tools, is feasible for implementation in resource-poor countries and can lead to rapid gains in the quality of case-management. IMCI is therefore likely to lead to rapid gains in child survival, health and development if adequate coverage levels can be achieved and maintained.