Mandatory enrollment of Medicaid recipients into managed care organizations (MCOs) in 1994 resulted in a major reduction in primary medical care provided by the Peninsula Health District (PHD) in southeastern Virginia. This article describes how the PHD responded proactively by changing from a predominantly primary care clinic practice to a population-based public health practice and changed the role of public health nursing. A participatory planning process involving all PHD employees carefully defined this new direction over several years. As public health care resources were redirected into preventive programs to serve the health needs of the entire community rather then the individual, a new intervention model evolved. The intervention model became the framework for program planning and implementation and has now been in use by the PHD for 3 years. The planning process used by the PHD to devise a population-based intervention model is described in this article.