This report is a synthesis of lessons learned about the early implementation phase of Integrated Management of Childhood Illness in four countries (Bolivia, El Salvador, Honduras, and Nicaragua). It is not an evaluation of the impact of the strategy on child health indicators, but rather a documentation of the processes and feedback from front-line staff in health facilities about their experiences. The specific objectives of this review were to identify the main achievements and difficulties and to summarize the lessons learned from the process of implementing IMCI in order to facilitate future implementation.