This article describes a flexible primary health care methodology which was developed by Andean Rural Health Care and its colleagues in Bolivia, South America. This methodology, the census-based, impact-oriented (CBIO) approach to primary health care, involves determining local health priorities as defined both by locally acquired epidemiologic information and by the local people themselves. The CBIO approach to primary health care is now functioning successfully at seven program sites in Bolivia, which together serve 75,000 people in urban and rural communities in three distinct cultural and ecological regions of the country. High levels of coverage of basic health services can be achieved through a system of 'epidemographic' surveillance of all families and through home delivery, when needed, of priority services to those at risk. When the services provided are based on local health priorities, when they are provided in a technically effective manner, and when the community has a strong partnership in planning, implementation and evaluation, then the CBIO approach to primary health care will lead to measurable health improvements as defined by changes in population-based rates of mortality and illness in the community. On the basis of our experience, we believe that the CBIO approach offers great potential for strengthening the effectiveness of local health programs in impoverished communities around the world in a way which fosters community ownership and, hence, long-term sustainability.