An estimated 10.8 million children under 5 continue to die each year in developing countries from causes easily treatable or preventable. Non governmental organizations (NGOs) are frontline implementers of low-cost and effective child health interventions, but their progress toward sustainable child health gains is a challenge to evaluate. This paper presents the Child Survival Sustainability Assessment (CSSA) methodology--a framework and process--to map progress towards sustainable child health from the community level and upward. The CSSA was developed with NGOs through a participatory process of research and dialogue. Commitment to sustainability requires a systematic and systemic consideration of human, social and organizational processes beyond a purely biomedical perspective. The CSSA is organized around three interrelated dimensions of evaluation: (1) health and health services; (2) capacity and viability of local organizations; (3) capacity of the community in its social ecological context. The CSSA uses a participatory, action-planning process, engaging a 'local system' of stakeholders in the contextual definition of objectives and indicators. Improved conditions measured in the three dimensions correspond to progress toward a sustainable health situation for the population. This framework opens new opportunities for evaluation and research design and places sustainability at the center of primary health care programming.